YO Handbook Part I 11 July 2024 PDF

RESTRICTED INDEX S No TOPIC PAGE NO 1. Theory of SA Fire 2-7 2. Theory of Normal Gp 8-15 3. Ballistics Of Small Arms Ammunition...

RESTRICTED INDEX S No TOPIC PAGE NO 1. Theory of SA Fire 2-7 2. Theory of Normal Gp 8-15 3. Ballistics Of Small Arms Ammunition 16-30 4. Principles of Auto Ops 31-59 5. Construction of DA Template 60-77 6. Intro to 7.62mm DSR 78-86 7. Bore-Sighting of 84mm RL Mk-III 87-93 8. Intro to ARC 94-102 9. Maint of Wpn, Kote Docu & Insp 103-115 10. Type of Rg & Conduct of Firing 116-128 11. Zeroing and Bore-Sighting of INSAS Rif and LMG 129-136 12. Taking Lead with INSAS Rif 137-140 13. Intro to RPO-A Flame Thrower 141-146 14. Rg Card 147-151 RESTRICTED  RESTRICTED 2 THEORY OF SA FIRE Intro 1. Wpns with caliber less than 25mm are categorised under SA in India (British categorize SAs as less than 20mm). Before going on the minor details and intricacies which form a part of this wpn, we shall see in this lec, some of the maj factor/ terms connected with SA fire, their application and influence on it. Aim 2. To teach the theory of SA fire and its application in marksmanship trg. Preview 3. For ease of understanding and better assimilation this lec will be covered in three parts:- (a) Part-I. Terms/Definitions. (b) Part-II. Application. (c) Part-III. Effect of weather on SA fire. PART-I: TERMS/ DEFINITIONS 4. Some of the maj terms connected with SA fire are given below: - (a) Caliber. Distance between two opposite lands is known as caliber. (b) Axis of Bore/Brl. It is an imaginary line passing through the center of the bore, joining the breech face and the muzzle end. (c) Line of elevation. The extension of axis of bore ahead of the muzzle before firing (after firing it becomes line of departure) is called line of elevation. (d) Line of Sight. An imaginary line joining the eye, center of rear sight aperture, foresight tip and the POA on the tgt. (e) Trajectory. The parabolic path taken by the CG of the bullet after exiting from the muzzle up to the tgt or where it falls on the grnd is called trajectory. It is parabolic in nature due to the combined effect of gravity and air resistance. (f) Line of Departure. Line of departure is the imaginary straight line, which the bullet would have taken on exiting from the muzzle. It is tangent to the trajectory of the bullet at its origin ie muzzle end. (g) Jump. When a bullet is fired, due to its mov through the brl, vibrations are produced, due to which the brl moves in the horizontal/ vertical plane. The mov of the brl in the vertical plan is termed jump: - RESTRICTED  RESTRICTED 3 (i) Positive Jump. The mov of the brl in the vertical plane over the line of elevation is called positive jump. (ii) Negative Jump. The mov of the brl in the vertical plane below the line of elevation is called negative jump. (h) Throw off. The mov of brl in the horizontal plane because of the vibrations is called throw off. Eg: AK- 47 has a throw off in the 2' O clock direction. To negate this a compensator has been added on as muzzle att in the 7’ O clock direction on the wpn. Another example is 9mm SMC with throw off in the lt direction. (j) Recoil. Every action has an equal and opposite reaction (Newton’s third law). The energy acting in the opposite direction to the mov of the bullet in the brl in the fwd direction is called recoil. 5. Angles at Wpn End. (a) Horizontal at muzzle. It is an imaginary plane parallel to the plane of the surface of the earth passing through the muzzle of the weapon. (b) Angle of Jump. It is the angle between the axis of brl when the wpn is laid for firing and axis of brl after firing or the line of departure. (c) QE (Quadrant Elevation). It is the angle between the axis of brl (Line of Elevation) before firing and the horizontal at muzzle. (d) Angle of Sight. It is the angle between the line of sight and the horizontal at muzzle. (i) Positive angle of sight- if POA above horizontal. (ii) Negative angle of sight- if POA below horizontal. (e) Angle of Elevation. The angle between the line of sight and axis of brl (Line of elevation) before firing is called angle of elevation. 6. Trajectory Related Terms (a) Culminating Pt. The highest pt on the trajectory is called the culminating pt. This ht is in relation to the Line of Sight. The culminating pt is formed at a rg, which is little more than half the rg of the tgts being fired at from the muzzle end. Eg: if tgt being fired is at 200m, the CP would be formed at approx 100m. It is also called as summit/vertex in high trajectory wpns (eg mors). (b) Ascending/Descending Branch. The part of the trajectory from the muzzle end up to the CP is called the ascending branch and the part from CP up to the tgt or the pt where it falls down on the grnd is called the descending branch. It is steeper than ascending branch. This increases as the rg increases. RESTRICTED  RESTRICTED 4 (c) First Catch. It is a pt on the trajectory, which is likely to contact the top most part of the tgt first. Therefore, it is directly dependent on the height of the tgt and the rg set on the wpn. There will be such a pt on the trajectory on both the ascending and descending branches of the trajectory (d) First Graze. It is that pt on the ground where the bullet falls after first catch. This is irrespective of whether the tgt has been hit at first catch or not. First graze occurs only in the descending branch of the trajectory. (e) Dangerous Space. The area/dist between the first catch and the first graze is called dangerous space. Dangerous space also occurs in the ascending branch, which is the dist between FC and the muzzle (in which area if the tgt comes it is likely to be hit). (f) Ricochet. When a bullet in its trajectory strikes a surface and changes its path once or more it is said to have ricocheted. 7. Angles at Tgt End. (a) Angle of Descent. It is the angle between the tangent to the trajectory and the horizontal at a particular pt on the trajectory. It can be measured at any pt on the descending branch of the trajectory. Also, the angle keeps increasing as the pt on the trajectory keeps moving down towards the grnd. (b) Angle of Fall. It is the angle between the tangent to the trajectory and the horizontal at the pt where descending branch of trajectory crosses the horizontal at muzzle. Angle of descent and angle of fall would be the same at the pt where the trajectory crosses the horizontal at muzzle. (c) Angle of Impact. It is the angle between the tangent to the trajectory and the normal to the tgt surface at the pt of impact. This depends on the inclination of the tgt/surface, which is struck. Lesser the angle of impact more will be the penetration. All these angles will be equal at the pt where trajectory crosses horizonal at muzzle in such a way that horizonal at muzzle also acts as normal to the tgt at the pt of impact. 8. Terms relating to Burst Fire (a) Cone of Fire. During burst fire each bullet has its own trajectory. These form an egg-shaped 'Khaka' in the air (basically because of the oscillation of the brl during burst fire). It is called a 'cone' because it is shaped in the form of a cone with the muzzle end acting as the apex and egg shape in the air as the base. (b) Beaten Zone. When this cone of fire of a burst falls on the ground, the area it covers is called the beaten zone. Usually the tgt being fired at falls in the centre of this BZ. BZ for LMG is: - (i) At 500m -175m x 2m (length x breadth) (ii) At 1000m - 115m x 4m RESTRICTED  RESTRICTED 5 (iii) The length of BZ decreases with increase in rg because of larger angle of descent and the width increases because of dispersion eff (due to wind action). (c) Dangerous Zone. The total area covered by dangerous space and beaten zone is called the dangerous Zone PART-II APPLICATION 9. QE and Angle of Sight. (a) More the QE and angle of sight more curved will be the trajectory and therefore more rg, and vice-versa. (b) More QE and angle of sight, less will be the dangerous space. (c) Lesser the QE, more the hit probability. 10. Angle of elevation. (a) The more the angle of elevation the more will be the rg achieved. (b) This axis of bore is always at an angle to the line of sight, because the min rg that can be applied on the back sight is 200m. If there was a way of applying 'zero' rg on the back sight, then the axis of bore and line of sight would be parallel. But to provide rg to the projectile the brl has to be raised at a particular angle (QE). This has been done by calibrating the line of sight and axis of bore. (c) When we increase rg on the back sight, the aperture moves up, the line of sight moves down wards. So to align this on the centre of the tgt the brl has to be raised, therefore an appropriate QE is obtained for that particular rg. 11. Factors Affecting Jump. (a) Stocking up/Tuning up. If stocking up/tuning up of the wpn is not carried out, there will be more vibrations and therefore more jump. (b) Oil in Brl/Cart. More gas, more vibration therefore more jump. (c) Pt of Sp. If the pt of sp is behind CG of wpn then the bullets tends to hit low. (eg, When the mag is rested on the grnd while firing the pt of sp is behind CG and therefore bullets hit low). Similarly, if pt of sp is ahead of CG than bullets tend to hit high. (CG in our rif/LMG is loc somewhere at the centre of the mag and a little below the axis of bore). (d) Firing with Bayonet. The muzzle becomes hy, therefore lesser jump (than normal), bullets hit below POA as CG of wpn shifts ahead. RESTRICTED  RESTRICTED 6 (e) Effect of Jump Reduced by Zeroing. Jump is inherent in the loc of a MPI in the case of a particular firer. Therefore, during zeroing when this MPI is shifted to a desired loc in relation to POA, the jump is catered for. Jump in a wpn can never be totally eradicated. Yes, it can be reduced to a large extent by proper hold. Also Jump cannot be reduced by zeroing. Only it’s effect can be negated by zeroing. 12. Factors Affecting Dangerous Space. (a) Rg. More the rg, more curved the trajectory, therefore sharper the angle of ascent and therefore lesser area between first catch and first graze i.e. Dangerous space. (b) Trajectory. Corollary to above. (c) Ht of Wpn. More the ht of wpn, more curved will be the trajectory to a wpn firing grazing fire on the same tgt (in comparison). Therefore, a sharper angle of descent and so lesser dangerous space. (Hence auto wpns should preferably be sited on the grnd floor while fighting in built up area. (d) Ht of Tgt. The more the ht of the tgt, the earlier will be first catch on the trajectory, therefore more area between first catch & first graze i.e. Dangerous space. (e) Configuration of Grnd Behind Tgt. (i) If rising - Less Dangerous Space. (ii) If sloping - More Dangerous Space. 13. Range-Estimation Permissible Error. (a) Range estimation is always a problem. But while firing burst fire where a BZ is achieved, permissible error in estimation of rg exists, which is half of the length of BZ. (b) Rg 500m. (i) BZ - 175m (Length) (ii) Round it off to 180m (iii) Now a tgt usually falls in the centre of the BZ. (iv) Therefore, 90m of the BZ exits ahead as well as behind the tgt. (c) Now if the firer in rg estimation is plus/minus 90m the tgt would still fall within the BZ and get hit. (which is 50% of the length of BZ) 14. Fixed line. (a) At 700x the CP of an LMG is 4 ½ ft. (b) Fixed line should not be chosen beyond 700m. (c) To ensure grazing fire and max DS, the POA on the object chosen for the fixed line should be at the bottom edge. RESTRICTED  RESTRICTED 7 PART III: EFFECT OF WEATHER 15. Weather affects the trajectories in the following manner. (a) Temp. (i) Cold Soaked Amn. In case of snow bound area, some amount of moisture is inherently present in the propellant. If the amn comes in contact with cold or gets soaked the amount of moisture increases. Therefore, rate of burning is slow, less gas energy op on the bullet, thus bullets tend to hit low because of lower trajectory. (ii) Amn out in the sun. Reverse of above. The inherent moisture dries up, rate of burning is more, gas op on bullet comparatively higher, thus bullets tend to hit high. (b) High Altitude. Rarer atmosphere affects the trajectory, lesser pressure on the bullet implies higher trajectory therefore bullets tend to hit higher. (c) Humidity. Humidity means rarer atmosphere, therefore less resistance of atmosphere on the bullets. MPI forms low. (d) Wind. Cross wind has a drastic effect on the path of bullet and aiming off would be required. Aiming of factor varies with rg and cross wind valiances. The bullets vel is not constant over the entire rg. Head wind and tail wind increase and decrease the angle of descent respectively and therefore MPI would shift downward and upward accordingly. This effect is marginal and no aiming off is desirable. (e) Lt. (i) Bright Sunlight. False (mirage effect) foresight over the actual one, the firer tends to align tip of false foresight with his LOS. The brl moves down and therefore the bullets hit low. Therefore, lt up sight up. (ii) Poor Lt. During poor lt, the foresight cannot be seen, but the base of foresight which is thicker is visible. Therefore, the firer aligns the base of foresight with his LOS. The brl moves up and bullets hit above. Therefore, lt down sight down. Conclusion 16. In this lec a broad overview was presented on the terms related to SAs, their application and factors that affect the flt of bullet. Further intricacies of the working of the wpn sys will be covered in the principle of Auto Ops. RESTRICTED  RESTRICTED 8 THEORY OF NORMAL GP AND SHOT GP ANALYSIS Intro 1. However, accurate the wpn, high quality of amn and skillful the firer be, no two shots pass through the same hole. A series of shots fired will form some sort of a pattern on the tgt and will be governed by the conditions of the rif, amn and skill of the firer, usually the last named. Also, during some phase of trg, a few firers will have more difficulty than the others in application of various firing techniques. Hence there are less skillful firers. 2. From the aspects mentioned earlier, it becomes imperative for a soldier to understand the Theory of Normal Gp and corrective analysis of the various gps formed, so that, he can correctly apply the knowledge when the need arises and become proficient in the handling and emp of his wpn. Aim 3. To teach the theory of normal gp, the tech of analysing a gp and correcting it. Parts 4. This lecture will be conducted in four parts: - (a) Part-I - Basics of good shooting. (b) Part-II - Gp and its Analysis. (c) Part-III - Corrective Ex. Part-I Basics of Good Shooting 5. It includes: - (a) Steady Hold. This helps in reducing wobble area, unnecessary movements and in absorbing recoil. (b) Correct Aiming. (i) Focusing. Human eye can focus at only one pt at any one time. (ii) Sight Alignment. Aligning of eye, centre of back sight aperture, with foresight tip. (iii) Sight Picture. When sight alignment gets aligned to POA on the tgt it is called sight picture. RESTRICTED  RESTRICTED 9 (iv) Correct Aiming Technique. Select the centre of rear sight aperture align it to the foresight tip and aim on the POA, then focus back on foresight till alignment is correct and press the trigger. (c) Trigger op. Obtaining first and second pull. (d) Natural Alignment. Human eye can align automatically to the centre of the tgt. During lying posn the tgt, rifle, left elbow, rt shoulder and rt heel should be in one line to achieve the natural alignment. (e) Correct follow through. PART-II GP AND ITS ANALYSIS 6. Definitions. (a) Gp. If a firer fires three or more than three rds with his wpn at one rg, same posn, maintaining the same hold and POA, then the pattern of bullets formed on the tgt is called a gp. (b) Normal Gp. It is imperative for a firer to know the normal gp that he is capable of firing with his wpn at any given rg. In order to understand this, take any firer and make him fire several gps from 100 yds from a given firing posn on a number of tgts spread over a period of time. The average size of the gps formed, would be the normal gp capability of the firer. The size of gp increases with the rg. 7. Causes for fmn of a Gp. The various causes of bullet dispersion leading to fmn of a gp and the fact that no two bullets pass through same hole are: - (a) Different MV for every bullet. (b) Different angles of dep. (c) Different atmospheric conditions. 8. Different MV. Different MV bring about a difference in rg and hence in trajectory. Difference in MV is due to: - (a) Difference in wt of propellant ch, shape and size of bullets. (b) Difference in propelling ch temp, which is dependent on air, and breech temp. (c) Difference in extent of brl heating. 9. Different Angles of Dep. These could be due to the following reasons: - (a) Throw off and jump in wpn. (b) Improper hold, prep of wpn, use of sp and jerky trigger op, changing the hold of wpn in between firing. (c) Angular oscillations of auto wpns due to the mov and shock of the moving parts. RESTRICTED  RESTRICTED 10 10. Different Atmospheric condition. Difference in atmospheric conditions like change in speed/direction of wind in between firing will affect the flt pattern of the bullet. The different conditions could be as follow: - (a) Direction of wind. (b) Speed of wind. (c) Bright lt conditions. (d) Poor lt conditions. (e) Humidity. 11. It is impossible to eliminate the causes which bring about dispersions and consequently, it is impossible to eliminate dispersion yet it can be decreased appreciably by the trg of the firer and proper prep for firing. 12. Location of MPI. Before a firer carries out his zeroing, firing of wpn is necessary for him to know the loc of MPI so that he is able to quickly bring his MPI to the centre of tgt/ desired POA. It must be borne in mind that a min of three bullets must be fired in order to gauge the correct MPI and that too after ensuring that the firer has not committed any mistake during firing. The effects of wind and vis must also be considered. Three basic methods/ways of finding out the MPI are as under: - (a) Calculation method. (b) Axis of dispersion method (c) Graphical method. 13. Graphical method. ________________________________ No of rds I Deviation ------------------------ I Vertical I Horizontal __________________________ 1. 3cm 1cm 2. 2cm 0cm 3. 2cm 2cm 4. 1cm 3cm 5. 0cm 1cm ______________________________________ Total 8cm 7cm ______________________________________ Avg 1.6cm 1.4cm _______________________________________ (i) Draw a vertical line through the lt / rt most hit of the gp. (ii) Draw a horizontal line through the upper most or the bottom most rd of the gp to intersect the vertical line. (iii) Take out the vertical and horizontal deviations of each rd (in cms) from the y-axis and x-axis. (iv) Add the deviations for all rds in the horizontal and vertical separately. RESTRICTED  RESTRICTED 11 (v) Determine the mean deviation ie horizontal and vertical by dividing the total, by the no of rds. (vi) Mark out this deviation (mean horizontal and vertical) from x- axis and y-axis that is the MPI of the gp. 14. Axis of Dispersion Method. This is used to locate the MPI of a large no of rds. Divide horizontally and vertically (numerically) the rds into two halves to obtain the MPI. It is the quickest method. 15. Calculation Method (i) Step One. Draw a line to join the first and sec shot. Then bisect this line. Thispt is the MPI of these two shots. (ii) Step Two. Join the MPI in step one to shot three by drawing a line. Now trisect this line and point closer to the last MPI (MPI of sketch) is the new MPI. (iii) Step Three. Join MPI of step 2 to shot 4 by drawing a line and divided this line into four equal parts. The pt nearest to MPI of step 1 is the new MPI. (iv) Follow the above procedure for the 5th, 6th and other shots to determine the MPI of the gp formed on the tgt. Analysis of various Gps 16. Shot gp analysis is done by loc the pattern of bullet holes on the tgt. The distance between the holes and the overall pattern of gp determines the proficiency of the firer. As a gen rule the smaller the pattern better is the shot gp. 17. The most unsatisfactory gps are usually those which are a direct result of incorrect sight alignment. That is at the time of firing, the firer either commits an error in sight alignment or placement of the aiming pt or a combination of both the errors. However, incorrect sight picture does not necessarily mean that is the only mistake in aiming. The following example explains this pt. (a) Incorrect application of trigger pr will always pull sights out of alignment and / or off the aiming pt. (b) Improper breathing or undue muscular strain can also cause aiming errors though these are less common mistakes than improper trigger cont. 18. Instrs and coaches should, therefore, keep in mind that improper application of any of the fundamental can disarrange the sight picture resulting in unsatisfactory gp. Therefore, it is essential that the firers be closely watched to find out which fundamental is being violated. Single shot Gp Analysis 19. The size and pattern of single shot gps will indicate the following errors: - RESTRICTED  RESTRICTED 12 (a) Long Vertical Gp. These are formed as a result of improper vertical sight alignment. That is the firer has kept the tip of the foresight either too high or low in respect to the imaginary centre of the backsight aperture. Long vertical gp is also formed as result of improper breathing tech while firing. (b) Long Horizontal Gp. These are formed as a result of improper horizontal sight alignment. That is the firer has kept foresight tip either to the lt or rt in respect to the imaginary centre of the backsight aperture. (c) Short Vertical Gp. These are as a result of incorrect selection of aiming pt. This gp is formed when the firer aligns his sight alignment above or below the aiming pt. Incorrect Sight Picture. (d) Short Horizontal Gp. These are formed when a firer aims to the lt or rt of the aiming pt. Incorrect Sight Picture. (e) Low rt or along 4 o'clock line. Such gps are formed when the firer, to make the rif fire at a certain time rapidly applies pressure on the trigger or jerks the triggers. (f) Low lt or along 7o'clock line. Such a gp is formed when a firer in order to take the recoil, just before the wpn fires, tenses his shoulder, muscle and moves the shoulder fwd or back. (g) Up lt or along 11 o'clock line. These are as a result of a firer reaching on to anticipated recoil and blast during the exit of the rd. The firer flinches, closes his eyes and moves his head downward due to fear. (h) Bifocal Gp. Such a gp is formed when the firer at times focuses his eye on the tip of the foresight and at times focuses on the pt of aim. Two distinct gps are formed on the tgt. (j) Scattered Gp. When the firer does not follow any basic fundamentals of firing, such a gp is formed. Burst Gp Analysis 20. The pattern of burst gp fired from LMG will indicate the following errors: (a) Elongated Vertical Gp below POA. This is formed when the firer constantly pushes the wpn fwd while firing. (b) Elongated Vertical Gp above POA. This is formed when the firer constantly pulls the wpn backwards while firing. (c) Two distinct Gp. During firing, when the firer gets conscious about his hold and tries to tighten/loosen it, smaller gps are formed at two different places on the tgt as a result of shift in brl. This is called seizing. RESTRICTED  RESTRICTED 13 PART-III CORRECTIVE MEASURES/EXS 21. Analysis of a shot gp will indicate firers who are having difficulty and need correction. These firers should be assigned the best qualified instrs, who will examine the firersgps and other data present in the progress folder and render suitable advice. However, so as to avoid a hasty conclusion, it will be best that the coach closely observes the firer firing a few rds or gps so that the exact causes of the errors are determined. Also, it is recommended that the coach first establishes or is convinced about the consistency of fire of the firer and only then goes about analyzing his fire and gps formed on the tgt. The following exs may be used to improve the various faults committed by firers. (a) Trigger Cont Ex. (i) Tin Disc Ex. This is an excellent method to correct soldiers trigger jerking habit because of improper breathing or muscular tension. This is a dry fire practice and standard firing posn can be used. When the firer has taken up his posn and cocked his wpn, the instr places a smaller size tin disc at the front end of the brl. On pressing the trigger, the tin disc should not fall if the firer is in a relaxed posn, breathing properly and squeezes the trigger as per the teaching. A one by one tgt must be placed for the firer to aim. (ii) Blank Tgt Ex. This is designed to correct firers who jerk the trigger once their sights are aligned to the aiming pt. The cause of the error is that the firer is concentrating more on the aiming pt than the sight alignment or trigger control. As soon as he thinks he has obtained correct sight picture he jerks the trigger. In order to remove this fault, the firer must learn that the aiming pt is of lesser importance in relation to sight alignment and trigger control. Removing the aiming pt and replacing a standard tgt with a blank sheet of paper having no aiming pt can best remove this. This will ensure that the firer does not hurry his shot. The instr will note an imdt improvement. Once the instr is satisfied, then the firer is made to fire one or two gps on to the std tgts for confirmation before being released from corrective instrs. (iii) Trigger Control Ex. This is to improve upon the trigger control of the firer. After he is in posn and ready to fire the coach places his own finger above the finger of the firer on the trigger and squeezes the trigger till it fires. In this way the firer gets the feeling of the proper squeezing action to be used, if both the fingers (firers and the coaches) do not fit inside the trigger guard than the trigger guard should be removed for this ex. (b) Ball and Dummy Ex. This ex should be used extensively to iden and confirm faults like bucking and flinching. The mag is filled with ball and dummy rds but the firer should not be aware of the same. During firing the mistakes like bucking, flinching and jerking can be identified/magnified when the firer flinches/ bucks and there is no recoil. This is also a good ex, which RESTRICTED  RESTRICTED 14 helps in making the firer aware of his mistake. After the fault has been identi- fied corrective exs can be given to the firer. (c) Aiming Box Ex. For this ex the SLR (without mag) is placed on a short aiming rest, which is of the ht of the firer. A 6"x6" white paper is placed on the aiming box at a dist of 10 m from the muzzle end. The firer takes posn behind the wpn and the coach takes posn on the aiming box. An aiming disc which is half black, half white and has a 3"x4" white aiming mark in the centre with a hole at the centre is used. The coach moves the disc over the white sheet on the aiming box as per the instrs of the firer who is aiming through the sights of the wpn on to the disc. As soon as the centre of the disc is aligned on to his sight picture the firer calls out ‘Nishan’ (or closes his fist). At this the instrmks out a pt on the sheet with the pencil through the hole on the disc. This process is repeated three times at the end of which three pts are obtained on the white sheet. If the size of this gp is more than 6mm than the firer is either committing a mistake in his sight alignment or the sight picture, more so sight alignment. Further analyzing the gp formed will confirm the mistake being committed by the firer. This can further be confirmed by using the aiming corrector. The aiming box ex should be conducted for the firer till such time he does not obtain a grouping capability of 6mm. (d) Aiming Corrector. A coach to find faults of sight alignment or sight picture uses this. The aiming corrector is put at the fwd edge of the butt of the wpn. The coach takes posn onto the rt of the firer and at rt angles to him. The firer takes aim and fires while the coach observes through the aiming corrector. (e) Small Arms/Trg Simulator (SATS). It is of US origin, presently being produced by BHEL. It gives out the errors of a firer in percentage and accurate analysis is carried out by the cmptr. 22. Seemingly, the pattern formed at the tgt is the direct out come of error committed by the firer yet this relationship is not mathematical. It never happens that a typical gp is formed by a typical error/fault. It is all a happy mix of various faults. That is why gp analysis is definitely an art acquired over a long pd of prac and not a formula based analysis. The analysis card is a rough guide for the coach. Besides it can never confer all possible mistakes or a combination thereof. The coach has better chances of catching a mistake/error while the firer is committing it by ob- serving the firer during firing shot gp. Analysis should generally be resorted to confirm/reject any obsn of coach during the firing stg. 23. As regards the burst gp analysis the extent of natural dispersion due to auto fire and the effect of firer's mistake, there upon calls for a close and contd diagnostic obsn of the firer (checking the posn, hold and other steps involved in firing). A firer may make a combination of errors ie vertical sight alignment and pushing LMG fwd or shift in sight picture and pushing the LMG fwd. More shot gp analysis could have hinted towards one mistake only but if the firer had been closely observed, the combination of faults being committed would have come to light. This goes to prove that short gp analysis is best used as a follow up of obsn already made in the firing stg. To be able to confirm conclusively whether the firer is pushing/pulling during the RESTRICTED  RESTRICTED 15 LMG burst fire, it is not mandatory to loc the first shot of the burst besides it is extremely difficult to loc the first shot. The loc of MPI in respect to the pt of aim and the pattern of burst would help in calling it a falling or rising gp. The above pattern coupled with the coach’s obsn of firer would assist in correctly analyzing the shot gp. Conclusion 24. A good firer is one who can maint his normal gp at any and every rg. During firing a firer should never forget his capability of normal gp. When a firer is able to achieve a good gp and the MPI is being formed at the centre of the tgt, than it could be said that he is a good firer. Also in order to achieve the desired firing results each ind should be able to analyze the shot gp and subsequently improve upon it keeping in view all factors of basic marksmanship trg. Record must be maint to enable instrs/coaches to review the firer’s performances. And finally it may be added that a soldier must be able to correctly and thoroughly understand the theory of normal gp and shot gp analysis if he is to effectively handle and emp his wpn to become a proficient firer. RESTRICTED  RESTRICTED 16 BALLISTICS IN SMALL ARMS AMN Introduction 1. The first stone hurled by prehistoric man was probably the earlier example of ballistics, the advantage of being able to throw further and with more power led to such devices such as sling and pears. Next came the how, and an extension at it called "Ballista" from which ballistics derive its name. In turn the word ballista owes its origin to a Greek word "Ballieu" meaning to "throw". 2. Therefore, to understand the design of SAA, it is essential to know, its behavior when inside the wpn, outside the weapon and finally when it strikes the tgt. Ballistics is the study of motion of projectiles during propulsion, free flight and impact. Aim 3. To introduce the ballistics in SA ammunition. Preview 4. The subject will be covered in the following parts:- (a) Part I - Definitions. (b) Part II - Internal Ballistics. (c) Part III - Intermediate Ballistics. (d) Part IV - External Ballistics. (e) Part V - Wound Ballistics. PART I – DEFINITIONS 5. Definitions of the types of ballistics are given as under: (a) Internal Ballistics. This is the study of events, which take place from the moment of ignition of the propellant to the time when the projectile leaves the muzzle end or the rocket reaches all burnt position during flt. The history of internal ballistics began with the use of gunpowder dating back to 1320. By the end of the 18th Century, the composition of gunpowder was fairly well standardized. Earlier attempt to measurable ballistics of the powder were made in by Hay in England where scientific study of op processes within the gun from the moment the burning of the propellant is initiated was studied. (b) Intermediate Ballistics. Study of transition from internal ballistics to external ballistics which occurs in vicinity of the gun barrel is called Intermediate ballistics. RESTRICTED  RESTRICTED 17 (c) External Ballistics. On leaving the gun and the influence of emergent gases during the free flight of the projectile in air/water, the forces acting on the projectile are mainly aerodynamics force of gravity. First theory in external ballistics was reasoned by Aristotle that no nominated body can move without a motive force unless it belonged to four natural elements i.e. fire, air, water and earth, however much change have come in subsequently. (d) Wound Ballistics. It is the study of motion of projectiles within the body and their wounding capacity. (e) Terminal Ballistics. It is the study of effect of projectile on the target. Terminal Ballistics depend on strike velocity, strike angle, type of projectile and target. It also includes body armour and is more relevant to anti-armour projectiles. PART-II INTERNAL BALLISTICS 6. Construction of a round (a) Base. The base is made of stronger material than the cartridge case. The base also houses the percussion cap. The base could be either fitted or crimped to the cartridge case. (b) Percussion cap. The percussion cap in made of material which ignites on impact. The cap composition is usually made up of fulminate of mercury. (c) Cartridge case. The cartridge case is usually made up of a brass- copper alloy (in a ratio of 70:30). The selection of cartridge case is dependent on its property to expand rapidly to hug the walls of the chamber to achieve obturation. (d) Propellant. Propellant is that chemical substance that is placed in a cartridge case of a round. It has a very fast rate of burning & produces intense heat. Propellants are of three different type and come is different shapes: RESTRICTED  RESTRICTED 18 (i) Single-Base. Nitro cellulose dissolved in either and alcohol. (ii) Double-Base. Nitrocellulose dissolved in nitro-glycerine. (iii) Triple-Base. Nitrocellulose dissolved in nitro-glycerine and nitro guanidine added. (e) Common shapes of propellant granules. (i) Disc. (ii) Cylindrical. (iii) Multi-tubular. (iv) Cord. (v) Ribbon. (vi) Slotted tube. (f) Bullet. The bullet is fitted to the cartridge case. The design of the bullet is based on the desired effect it should have on the target end. This effect depends upon: (i) Shape. (ii) Size. (iii) Construction. (iv) Velocity. (v) Stability. (vi) Design of the bullet. (aa) Soft bullet. (ab) Stable jacketed. (ac) Unstable jacketed. 7. Type of Projectiles. (a) Bore/Cal Projectiles. These are conventional arty shells or bullets whose diameter is equal or slightly more/less than caliber of the wpn. They generally have driving bands on them for setup/obturation. Projectiles not having driving bands depend upon high pressure gases for obturation/setup. RESTRICTED  RESTRICTED 19 (b) Sabot/Sub Cal Projectiles. Any projectile that is fired using a sabot. (Sabot is a device which is used to fire projectiles of diameter lesser than caliber of the wpn). They have advantages both in external and terminal ballistics. For e.g. due to Sabot lesser projections are made on projectile itself, hence it is subjected to lesser excrescence drag. Similarly, Sabots can also be used to achieve greater terminal velocities (APFSDS). Sabots can be discarded radially or axially. Axially due to drag and radially due to spin/gas flow. (c) Shot/Slug. Large no of projectiles within a single rd/bigger projectile. They are blasted towards the tgt as indl projectiles. Commonly used in shot guns. Flechette is a kind of Shot Projectile. 8. Type of Primers. (a) Rim Fire. In Rimfire Primers, the rim itself acts as primer cap as well as the anvil. The priming compound is housed between the layers of rim and on striking by fire pin it is crushed between the two layers leading to production of flash. (b) Centre Fire. Priming compound is housed inside theprimer cap which I placed in the center of Primer. On crushing the center of cart case by firing pin, priming compound is igninted. It may be Boxer or Berden type. In Berdan type Anvil is part of cart case whereas in Boxer Type Anvil is housed inside primer cap. Ignintion Sequence 9. It is necessary to study what happens in a modern firearm when the propellant is initiated and the bullet moves in the barrel. The details of the composition of the cart will be explained later. However, once the chamber is closed and the firing pin strikes the primer cap at the base of the cartridge, which on ignition burns the propellant resulting in production of hot gases which increase the pressure in the case resulting in the bullet being move fwd and spun by the rifling as it picks up velocity. 10. Shot Start Pressure. This is the pressure generated sufficient to move the bullet from the case and up the bore. Gas is generated at tremendous pressure. The volume of the gas is greater than the space created by the projectile till it moves a certain distance and peak pressure be reached. The propellant gas pressure is inversely proportional to the heat retained by the gases divided by the volume of propellant gases. 11. Peak Pressure. This is the maximum pressure generated but the gases in the bore. After this the rate of increase of space in the barrel is greater than gas generation and the pressure falls. Peak pressure is dependent on the following factors: - (a) Rapid liberation of Gases. RESTRICTED  RESTRICTED 20 (i) Dependent on total surface area of propellant granules (Piobert's Law). (ii) High value of Force Constant. Depends upon the composition of the propellant. Double Base and Triple Base propellant have a higher force constant than Single Base. The value of the force constant is found by burning a measured mass of propellant in a strong air tight chamber known as a closed - vessel. The amount of energy released by a certain mass of propellant is related to its force constant. (iii) Fast burning rate. (b) High Projectile Mass. (i) This is relative to the bore and the propellant. (ii) Greater projectile mass resists acceleration resulting in build up of pressure. 12. All Burnt Point. This is the moment when the propellant is burnt. The position of the projectile is dependent on peak pressure. The greater the burning rate the faster the all burnt. In case all burnt is early, propulsive efficiency increases, muzzle blast is reduced as well as flash and there is increased consistency of muzzle velocity. This is because available gases act over greater distance. It is for this reason that long barrels have this same effect as the gases are made to act over a greater distance. 13. Pressure Time Curve. To recapitulate lets go over the sequence once again. (Data enumerated below is for 7.62 x 51mm amn) (a) Once firing pin/striker hits the cap composition the propellant gases get ignited. (b) The pressure increases to 5 tons/sq inch and that's called the shot start pressure. (c) The bullet starts to move up the barrel and the volume of available gases increases. (d) Once the projectile moves approx. 1/10 the length of the barrel 2/4 milli seconds, peak pressure is reached at 22 tones/sq inch. (e) The bullet starts traveling faster than the expansion of gases and pressure falls. (f) Obturation and set up occur (rewarded and forward move of gases is prevented). (g) Spin is imparted to the bullet due to rifling and approx. 15 degree of the kinetic energy is used up. RESTRICTED  RESTRICTED 21 (h) All burnt is reached in approx. one millisecond and the projectile continues its acceleration. (j) Bullets leaves the barrel in an approx. 1.5 millisecond at 1/6 the peak pressure. (k) The gases give further acceleration to the bullet up to few caliber lengths and at 4 milliseconds the pressure in the muzzle falls to atmospheric levels. 14. Relationship between pressure, velocity & time. Ref to fig of time and space curve: 15. Distribution of energy. (a) The approximate distribution of energy at the end of the firing sequence in as follows: - (i) Motion of projectile - 32% (ii) Motion of propellant gases - 3% (iii) Frictional losses - 3% (iv) Heat loss to gun barrel - 20% (v) Heat retained by propellant gases- 42% Total - 100% RESTRICTED  RESTRICTED 22 (b) The gun thereby has achieved its function with utilization of 20-30% of the energy. (c) Other minor effects on efficiency of the gun: (i) Energy loss to provide rotation/spin 0.15% (ii) Recoil motion -0.02-.05%. 16. Factors affecting ABP (All Burnt Point). (a) Exact instant for each granule is dependent on local conditions. (i) ABP. Moment at which all of propellant has been burnt. (ii) This happens almost simultaneously for all the granules though the exact instant for each granule will be dependent on its local condition within the gun. (b) ABP also depends on Peak Pressure. As burning rate is proportional to pressure (Saint Roberts Rule). (i) High Peak Pressure - All Burnt Point early. (ii) Low Peak Pressure - All Burnt Point late. (c) If ABP early:- (i) Increased propulsive efficiency of all the available propellant gases will propel the bullet for a longer distance along the barrel. Longer barrel helps, but frictional force should not over-come it. (ii) Reduced muzzle flash and blast. (iii) Consistency in muzzle velocity. (aa) On observation it was seen that greatest variation in projectile velocities occurred at the position of ABP. (ab) The variation in velocities lessens towards the muzzle, so the longer the projectile travels after ABP the less the variation in muzzle velocity. (d) If ABP is not reached. Large quantity of unburnt propellant resulting:- (i) Reduced propulsive efficiency. (ii) Intense muzzle flash. RESTRICTED  RESTRICTED 23 17. Factors affecting Internal Ballistics. (a) Propellant Energy. Dependant on following factors: (i) Charge weight. (ii) Quality or type of propellant (iii) Charge temperature. (iv) Space in which charge is enclose. (b) Length & diameter of barrel. (i) Length - more length better propulsive efficiency. (ii) Volume available - related to volume available for expansion of gases. (c) Projectile. (i) Mass. Affects PP & friction surface increases. (ii) Material. Friction with barrel more/less. (iii) Shape. Boat tailing adversely affects ‘Set Up’. (d) The cartridge case. Material used will decide effectiveness of obturation. PART III- INTERMEDIATE BALLISTICS 18. Intermediate ballistics is the study of transition from internal ballistics to external ballistics. This occurs at the vicinity of the gun muzzle. The distribution of energy at muzzle can be simplified down to: (a) Motion of projectile - 30% (b) Energy of the propellant gases - 40% (c) Heat retained by the gun barrel - 25% 19. Roughly 70% of the available energy passes through the muzzle. The majority of this is carried in the form of heat, pressure and motion. Even after the muzzle exit the behaviour of gases has considerable influence on the projectile and gun motion. 20. The gas flow field near muzzle. The release of high pressure gas from the muzzle causes turbulence as it mixes with the ambient air. The resultant pressure RESTRICTED  RESTRICTED 24 wave radiates at the speed of sound as noise. However during firing, the gas temp, pressure and density vary considerably at the vicinity of the muzzle whereby the speed of sound too varies. 21. Shock wave. Shock wave in simple forms is an intense sound wave. Due to the move of shock wave, there is an increase in temperature of the medium (air) which results in an increase in speed of sound, consequently shock waves travel faster than the speed of sound of lower intensity. Conversely shock wave can be defined as a sound wave of sufficient intensity of self-induced velocity significantly greater than that of speed of sound (i.e. 332 m/s). 22. Blast Shock Wave. When the gases from the barrel come out, noise is generated by the turbulent mixing of gases which travels both away from the muzzle and towards it. When the projectile exits from the gun high pressure is suddenly released from the muzzle, known as the blast shock wave. This wave travels at speed slightly greater than that of sound and is heard as a sonic bang. 23. Bottle Shock. The incoming noise forms a shock wave which travels towards the muzzle against the out flow of gases. Near the muzzle at one time the speed of incoming shock wave may equal the speed of out flow of gases, at this stage the incoming shockwave makes no head way and forms a “quasi-static shock wave”. The quasi static shock is bottle shaped and it is also referred as bottle shock. It has the following parts: (a) Barrel Shock. The curved sides of the bottle shock which extend from the muzzle are called the barrel shock. (b) Mach Disc. The almost flat base of the bottle shock is called the mach disc. 24. The size of the bottle shock increases as the velocity of the out flowing gas increases. As the gas velocity of the gas falls, the bottle shock shrinks and eventually disappears into the muzzle. Muzzle gas flow field during firing 25. The muzzle gas flow field during firing consists of two phases: (a) The Precursor Blast Field. The precursor blast is formed prior to exit of the projectile. The components which from this blast field are: (i) The propellant gases which escape prior to set up and during move of projectile during its move along the barrel. (ii) The column of air within the barrel which is pushed out. (iii) The shock-wave formed just ahead the projectile travels along the bore, and is released as a near spherical precursor blast shock at the muzzle. RESTRICTED  RESTRICTED 25 (iv) Once the out flowing air velocity is sufficient a small bottle shock is formed about the muzzle, growing in size as the flow velocity increases. (b) The Main Blast. The blast field that follows the projectile as high propellant gases ejected into the air: (i) The projectile emerges from the barrel, followed by release of high pressure propellant gases into the atmosphere. (ii) Initially the main blast shock field is highly non spherical as it is distorted by the presence of the bullet and the high velocity flow of gases. (iii) The propellant gases rapidly expand, accelerating to velocities much greater than that of the projectile which provides slight delay in acceleration of the projectile for several calibre distance from the muzzle. (iv) The muzzle gas flow as such can also have an adverse effect on the accuracy of the gun, causing abnormal yaw in the projectile. (v) A new large bottle shock is formed around the muzzle. As the velocity of out flowing gases reduces, the bottle shock shrinks and withdraws within the barrel. (vi) When the projectile is supersonic, it will, in the meantime pass through the blast field. (vii) Owing to the high intensity, the blast shock waves travel faster than the speed of sound and so tend to catch up with the less intense precursor blast shock. (viii) The figures below show three phases is the development of blast field after projectile exit. The initial formation of shock waves shortly after projectile exit RESTRICTED  RESTRICTED 26 Final phase of the blast field before contraction of the Bottle Shock and Mach Disc 26. Blast Suppression. In addition to the blast shock waves, a flash blast is caused on account of secondary flash because of heating and expansion of gases. To some extent blast shock may be suppressed by silencers which reduce the intensity of muzzle blast. 27. Reducing Recoil. Recoil is on account of the rear ward motion of the gun in reaction to forward motion of the projectile and propellant gases. A gun normally attains half the recoil energy by projectile exit and the balance by the rapid out flow of gases. By reflecting gases rearwards (through muzzle breaks), the forward thrust on the gun may be reduced from 50-25%. 28. Flash. This is the light in the vicinity of the muzzle caused by propellant gases on account of chemical reaction with air. The following occurs: (a) Pre-flash. Caused by escaped gases prior to exit of projectile from the barrel. (b) Primary flash. This is caused on exit of the projectile on account of high gas temperature leading to visible radiation. (c) Intermediate flash. The recompression of gases on passage through the Mach disc leads to intermediate flash. (d) Secondary flash. The ignition of hot compatible gases i.e., Hydrogen and carbon monoxide on mixing with oxygen. This is very bright in large calibre weapons but does not take place in small calibre weapons as gas ignition does not occur. (e) Incandescene. Remnants of hot propellant gases may be seen as a long streak of incandescent light. 29. Flash suppression is possible by following means: RESTRICTED  RESTRICTED 27 (a) Muzzle devices. By suppression and dispersion of barrel shock and mach disc they reduce the intermediate flash. (b) Propellants. By having triple base propellants having inert Nitrogen and reducing overall temperature and hence combustion. This however creates a lot of smoke. (c) Additives. By adding potassium and sodium salts to propellants and thus prevent the formation and burning of Hydrogen. This however creates a lot of smoke. PART–IV : EXTERNAL BALLISTICS 30. The factors which affect external ballistics are basically divided into two categories, one those which are associated with the bullet itself and others associated with the medium (Air in case of small arms) through which the projectile is traveling: (a) Related to the bullet. (i) Mass of the bullet. (ii) Calibre of the bullet. (iii) Shape of the bullet. (iv) Spin rate given to the bullet. (b) Related to the medium of traveling. (i) Air density. (ii) Temperature. (iii) Air pressure. (c) Aerodynamic factors. (i) Air resistance. (ii) Yaw. (iii) Drift. 31. Air Resistance. It is the retarding force acting in the opposite direction of projectile velocity. The air resistance acts in the following ways:- RESTRICTED  RESTRICTED 28 (a) Head Resistance or Forebody Drag. As the projectile moves through the air, the air is displaced. The energy needed to displace this air causes continuous drawl on initial energy given to the bullet, thus causing it to loose velocity. More blunt the nose of the projectile, higher the drag. (b) Base Drag. When the projectile travels at a very great speed in the air, it causes the vacuum behind it because the air flow cannot return quickly enough to fill up space behind the projectile. The consequence is suction effect or the base drag as well as regional turbulence. (c) Skin Friction. The resistance caused by air adhering to the projectile. This is less effective in small projectile & polished surfaces. (d) Excrescence Drag. Caused by unnecessary projections or protrusions on the projectile. 32. Methods to Reduce Resistance. (a) Boat Tailing. Streamlining of the base. It allows the air to flow closer to the base thereby reducing the vacuum behind the bullet and thus reduces the base drag. (b) Nose Shape. Longer the head the less the fore body drag. (c) Base Bleed. Not in small calibre projectiles. Using slow burning propellant at the base to reduce the vacuum. 33. Yaw. When the bullet is fired from the rifle, its axis does not tie exactly along the trajectory, which is the path of its centre of mass. The angle between the axis of projectile and tangent to the trajectory is called angle of yaw. Yaw affects the bullet in three ways: (a) Drag. Greater the yaw greater the drag. It retards the motion of the projectile and multiplies with range. (b) Crosswind Force. This force acts perpendicular to the yaw and trajectory and in the direction of yaw. It is of zero magnitude at zero yaw and increases with the ltd angle of yaw occurring during flight. It is similar to lift. (c) Overturning Moment. In a projectile the centre of pressure is not at the centre of mass resulting in overturning move which is stabilized by spin or fins. 34. Drift. A spun projectile will be found to deviate laterally from the original direction imparted to it by the gun. This lateral deviation is drift. In practice this lateral deviation is made up of two parts:- (a) Drift due to equilibrium yaw for spun projectiles while deviating laterally. (b) Drift due in relation to the earth, which is not applicable in case of small arms. RESTRICTED  RESTRICTED 29 35. Methods of Stabilization. (a) Fins. They bring the centre of pressure behind the centre of mass. As the rd/ bomb is fired, the nose dips down due to gravity and the fins rises up. The fins provide more cross sectional area for wind force to act upon which swings the bomb/rd around its centre of mass and the nose rise again. This rising and dipping of nose continues till the descending br. In the ddescending br, after a certain period, the combined force exerted by mass and gravity overcomes the wind force and hence the nose does not rise again, thereby ensuring that the bomb hits nose first. (b) Spin. On account of the requirement of having a strong base to withstand high pressure and a pointed nose to reduce fore body drag. the centre of mass is further to the base. While the centre of pressure is nearer to the base resulting in instability. Rotating the bullet produces gyroscopic forces i.e. like a top, resulting in stability. A gyroscope has the property that it resists any attempt to change the initial dirn imparted to it. So when the bullet began to Overturn due to Yaw and Drift, the gyroscopic forces of bullet resist that change and keep the bullet nose pointed towards initial dirn i.e. towards tgt. PART V: WOUND BALLISTICS 36. A wound results from the absorption of energy imparted by the bullet when it strikes and penetrates tissue. There effects depends upon size, shape, composition, Velocity and stability of the bullet. The soft tissue of the body is 800-900 times denser than air. Therefore when the bullet hits these tissues it nearly always becomes unstable. Any angle of yaw that is present will be greatly increased with a subsequent increase in damage. The main aim of designer is to have a balance between terminal power, which should not be that much that the bullet crosses the body and the velocity required for accuracy. When the bullet enters the body and lodges itself it is called a lodging bullet. Such a bullet causes maximum wound effect since max energy can be transfer to the target. Some bullets enter the body and exit from the other end. But by the time they exit, they would have lost some energy, thus when they leave the body, they cause a big wound which is called explosive wound. A stable bullet only transfers 10-20 % of its energy on passage through the body while unstable bullets transfers 60-70% of energy. 37. Causes of Injury. (a) Laceration & Crushing. This is the main effect of a subsonic projectile and only tissues directly hit are damaged. Injury is generally not serious unless a vital organ is hit. (b) Stress Waves. A high velocity bullet when striking compresses the medium in front of it which moves away as a stress wave in a spherical form. The velocity of the wave is equal to that of sound. The change is pressure causes damage to nerves in a considerable area. RESTRICTED  RESTRICTED 30 (c) Temporary Cavitation. A high velocity bullets momentum is transferred to the surrounding tissue which on passage of the projectile moves and oscillates creating a cavity temporarily 30-40 times the size of the projectile. This oscillation results in severe damage outside the immediate path of the projectile. The shape of the cavity is ellipsoid. Because of the atmospheric pressure bacteria, clothing etc. are sucked in. Higher the velocity, greater the cavity. 38. The Projectile Design. A soft nosed bullet will flatten on impact creating a greater surface contact area and greater retardation. This was the case with the old..303 bullet & the present Russian 7.62 mm bullet. An unstable jacketed bullet will release energy later as it yaws while a stable jacketed bullet will dissipate energy later resulting in a longer wound track. The ideal would be having a high impact energy without the projectile leaving the body. This can be ensured by shaping the projectile (keeping the Geneva Conventions in view) so that: (a) It breaks on impact on target, thus smaller portions have less velocity. (b) Deforms in a less streamlined shape. (c) Becomes unstable on entering from air to denser medium. 39. Factors affecting Lethality. (a) Mass of bullet. (b) Velocity of bullet. (c) Rate of transfer of energy. (d) Location of strike. (e) Cross section of strike. (f) Penetration achieved. (g) Stability of projectile. (h) Elasticity / density of body. (j) Damage caused. (k) Kinetic Energy of bullet. Conclusion 40. Ballistics is a science in itself. However keeping in view the scope of the course it must be limited to the contents only. The subject requires to be studied in conjunction with the related aspects of cycle of operation for better comprehension. RESTRICTED  RESTRICTED 31 PRINCIPLES OF AUTOMATIC OPERATIONS Introduction 1. To be able to understand the mechanics of working of our wpn systems it is imperative that we have complete knowledge of each and every component of a wpn, its effect on the working, the various types of operating principles and their effect on the design of a wpn system. This lecture is basically Aim plus, but nevertheless important. As wpn qualified instructors you should be in complete picture of all the mechanics that take place when a rd is fired, what causes stoppages and recommend possible changes in design characteristics for better functioning of wpn when they come to you for trails/use. Preview 2. This study will be carried out in six parts:- (a) Part I. Cycle of Operation and Safety in Weapons. (b) Part II. Operating Mechanism. (c) Part III. Gas Operation. (d) Part IV. Recoil System of Operation. (e) Part V. Blow Back System of Operation. PART I : CYCLE OF OPERATIONS AND SAFETY IN WEAPONS 3. Cycle of Operations. In a weapon, after a round has been fired, certain actions have to be carried out before the next round can be fired. First of all the spent case (the fired case), inside the chamber has to be removed. For this, the spent case is to be extracted and ejected out of the gun body. Once the case has been removed, the leading round from the magazine has to be fed inside the chamber. After the new round is fully seated in the chamber the breech block has to be locked to facilitate the further operation of the firing mechanism to fire next round. To complete this process recoiling (moving) parts are required to move back by the complete cartridge length. This complete process is known as cycle of operation. There are eight major steps which are given below - (a) The breech block is unlocked. The breech block which was locked before firing is unlocked so that it can start moving back. (b) The breech block is retracted. To extract the fired case which is inside the chamber the breech block has to move back. Hence the breech block starts moving back, or in other words breech block is retracted. RESTRICTED  RESTRICTED 32 (c) The empty case is extracted from the chamber. When the breech block starts moving back, the extractor which is part of breech block holds the fired case and pulls it along with it. Hence the fire case is extracted from the chamber. (d) The empty case is ejected from the gun body. The case which has been extracted from the chamber has to be ejected out of the gun body. For this there is an ejector in the gun body. The empty case strikes against it and is ejected through the ejection slot. The direction in which it will be ejected depends on the placement of extractor and ejector. (e) The return spring is compressed to store energy. The moving parts which have moved back need to be pushed forward. For this the return spring which is inside the butt is compressed and energy is stored in it. (LMG 18 lbs ft & Rifle 13-14 lbs ft). (f) The firing mechanism is cocked. Depending upon the design of weapon the firing mechanism which had been operated to fire the last round has to be cocked. This can be done either during the rearward movement of the moving parts like in case of rifle 7.62mm SLR or it can be done during the forward move of moving parts. In 303 rifle when the bolt is pushed forward the firing mechanism is cocked. There are certain weapons like LMG in which there is no separate firing mechanism which has to be cocked. In such weapons the combination of trigger allows the moving parts to move forward and piston post which is part of breech block pushing the firing pin forward strikes the primer cap. This combination can be called firing mechanism. (g) The next round is fed in position for feeding. When the moving parts move forward, the feed piece of breech block takes the leading round from the magazine and with the help of bullet guide pushes it inside the chamber. This action is known as feeding. (h) The round is chambered. During the final action of feeding when the round is fully seated inside the chamber it is known as chambering. The difference between feeding and chambering is that in feeding the cartridge is aligned with the chamber i.e. part of the cartridge is inside the chamber and a portion is outside, where as in chambering, the round is fully seated in the chamber. (j) Breech is locked. After the round is fully seated inside the chamber and breech block has completed its forward travel, there is a requirement of locking the breech. (k) The firing mechanism is operated. In the final stage of the cycle, the firing mechanism is operated to fire the round. 4. This is the basic cycle but depending on the design of the weapon there may be a change in the order of events or some parts of the cycle may be omitted entirely, e.g. in certain weapons operating on blow back system, locking and unlocking will be omitted. RESTRICTED  RESTRICTED 33 5. Based on the Cycle of Operations, weapons can be classified into three types as follows: (a) Manually Operated Weapons. These are those weapons where the cycle of operation is completed manually by the firer.e.g.303 or 7.62mm bolt action rifle. After firing the round the firer physically lifts the bolt up. By doing so he unlocks the bolt that had been locked before firing. After having unlocked the bolt he pulls it back. During the rearward movement of bolt, extraction and ejection take place. After the firer has pulled the bolt completely back, he pushes it forward. During the forward movement the firing mechanism is cocked, the feed piece takes the top most round from the magazine and loads it into the chamber. The bolt is locked to the weapon by the forward rotation. (b) Semi-Automatic Weapons. These are those weapons where the cycle of operation, except operation of firing mechanism is completed automatically. In semi-automatic weapons the trigger is required to be pressed for operating the firing mechanism to fire the next round. (c) Automatic Weapons. These are those weapons where the complete cycle of operation is completed automatically that includes firing also. Such a weapon will keep firing till such time the trigger is kept pressed. Design wise there is hardly any difference in automatic or semi-automatic weapons. Most of the automatic weapons can be made semi-automatic by changing the position of the change lever. 6. Safety in weapons. There are two types of safety devices in a weapon: (a) Applied safety. Applied safety is the one which is applied manually. This is primarily to prevent accidental fire in a weapon. Safety catch or change lever is an applied safety device. By putting a safety catch or change lever on safe the operations of firing mechanism is obstructed or in other words firing mechanism become inoperative. After applying safety catch weapon will not fire even if there is a round in the chamber. Examples are as follows: - (i) Safety catch/change lever. (ii) Trigger guard. (iii) Grip safety. As found in Uzi sub machine gun. It has a protruding lug on the rear side of the pistol grip. When the firer obtains proper hold on the wpn this lug gets pressed in and it is only then that the firing mech becomes free to be operated. (iv) Mag safety. (b) Mechanical safety. It is an inbuilt mechanical arrangement incorporated in the design of the weapon to ensure: (i) A round cannot be fired until it is fully supported in the chamber end. RESTRICTED  RESTRICTED 34 (ii) The support cannot be removed until there is safe pressure in the chamber, safe pressure here is 2 TSI. The above definition implies: (aa) The cap cannot be struck until the round is fully seated in the chamber. (ab) Some suitable device is employed to provide support to the base of round before the cap is initiated. (ac) A period of delay is incorporated to allow the pressure in chamber to drop to a safe level before it is removed. 7. From the definition it is quite clear that the mechanical safety is incorporated in the design itself that means the firers do not have to do anything. 8. When a firing mechanism is operated the propellant inside cartridge case is ignited leading to rapid decomposition of propellant. Pressure in the cartridge case increases to the tune of 22 to 23 TSI (for 7.62 x 51mm amn). The cartridge case itself is not strong enough to withstand such high pressure and it should explode or burst open. But this doesn’t happen. 9. When pressure of 22 TSI is generated inside cartridge cases the case itself is enclosed inside the chamber. The pressure which is applied radially is contained by the chamber walls which are strong enough to withstand a pressure up to 60 TSI. The pressure acting in the forward direction is used for doing useful work, i.e. pushing the bullet forward. The problem is how to hold the pressure which is acting the rearward direction. As this pressure is more than 20 TSI which is more than what the unsupported cartridge case can withstand, it is essential for the safety of the firer and to prevent damage to the weapon that the cartridge is fully supported at the base. This is done by locking the breech block with the gun body. Breech block after completing its forward travel comes to rest with its front face almost touching the face of cartridge case. Now if the breech block is locked with the gun body any amount of pressure exerted on the breech face will not be able to move it back. Hence cartridge case base remains supported. On the contrary, had the premature move of cartridge case occurred due to absence of support, the weaker portions of cartridge case would have exploded. As a result weapon would have been unsafe to fire. 10. Some additional safety is also required as the weapon is locked. The designer must so arrange his weapon that in no conceivable circumstance it is possible either for the cap to be struck before the cartridge is fully supported or for the support to be withdrawn before the pressure has dropped to the level considered to be safe. How this is ensured to make weapon 100% safe, will be covered in mechanical safety in rifle 7.62mm SLR. Locking the weapon alone is not safe enough. To ensure cap is not struck before a weapon is locked, an inbuilt mechanism is required to be designed. This is achieved in case of SLR through safety sear. Safety sear will get pressed only when breech is locked with body of SLR. Trigger will operate hammer only when safety sear has been pressed. RESTRICTED  RESTRICTED 35 Locking 11. Methods of Locking. To ensure mechanical safety locking of breech block is a must. There are various methods by which breech can be locked. The most common ones are given as follows:- (a) Rotating Bolt. In this type of locking mechanism after feeding the round inside the chamber the bolt rotates on its axis. Once the bolt rotates on its axis the cam of the bolt gets locked with the locking shoulders made in the body of the weapon The complete arrangement is so made that hammer will not contact the firing pin till such time the bolt rotates on its axis. Unlike the tilting block in which the locking is at the rear end of the BB in case of rotating bolt locking takes place at the fwd end of the BB. This has two advantages. The pr acting in the rearward direction is not acting on the complete BB (as in case of the rear end being locked), but is being stopped by the front portions of the BB, as a result the rear portion ie behind the locking lug does not need to be made heavy, and the wpn is lighter. Some of the weapons which have rotating type of bolt are: (i).303 rifle bolt action. (ii) 7.62mm bolt action. (iii) AR-15. (iv) M-16. (v) AK-47 Chinese rifle. (b) The Toggle Joint Lock. This locking device has two arms. The longer one is pivoted on the breech block and the shorter one on the barrel extension. Two arms are joined to a crank axis which floats freely. The main characteristic of crank is free to hold in the upward direction. Some of the weapons in which toggle joint locking mechanism are: (i) Vickers MG. (ii) Lugar 9 mm SL. (iii) 9mm Pistol. (c) The Tilting Block. In tilting block type of locking mechanism, the breech either tilts up or tilts down and the locking shoulder gets locked with the locking edges in the gun body after the breech has completed its forward motion. During this move either the breech block is tilted up with the help of locking cam like in case of 762mm LMG or is tilted down or the locked edges get locked with locking shoulders in the gun body. The examples of this are (i) Downward Tilt of BB. During the final forward mov of the slide the rear portion of the slide pushes the breech block downwards into the RESTRICTED  RESTRICTED 36 locking recess provided in the body of the wpn and the Breech block is locked. Eg 7.62mm SLR. (ii) Upward Tilt of BB. During the final fwd mov of the carrier gp the piston cam lifts the breech block upwards into the locking recess provided in the body of the wpn and hence the breech block is locked. Eg 7.62mm LMG. (d) Sliding Breech Block. In sliding block the arrangement is so made that the block can only move on sides. When the breech block stands behind the case there is no provision to move back. It can only move on side, hence the locking takes place. The chief advantage of this type of mechanism is that it shortens the body length of the gun. The total length that is reduced is the sum total of complete length of the round, the length of breech block and the length of the compressed return spring. This type of locking mechanism is very common in Arty guns e.g. 25 pounder gun. It is also used in machine guns used on tanks or APCs where the inboard is less. The example of this type of locking mechanism is M-73 tank machine gun. (e) The Projecting Lug Device. Lug locking type of locking mechanism is simple. Some form of locking lug is forced out of the block to engage in a suitable recess in the body of the gun. For unlocking the lug moves back in the breech block. This can be vice-versa also. The lug may come out of the body of the weapon and stand behind the breech block as in the case of a door knob. The way you move your door knob to get the bolt engaged in the locking recess. This type of locking mechanism is very common. The most common example is.30 browning MG, 9mm pistol. 12. Type of Breech Mechanism. Whenever a weapon is designed the first and foremost thing that is planned is how to make the weapon mechanically safe. No weapon can be designed to function without mechanical safety. To understand mechanical safety in these weapons first it is important to understand that there are two types of breech mechanisms: - (a) Open Breech Weapons. These are those weapons where same components carry the round to the chamber and fire. These weapons do not have a hammer or a separate firing mechanism like in case of 7.62mm LMG. When the trigger is pressed the moving parts are released and they move forward under the tension of their return spring. During this forward movement they take the leading round from the magazine and feed it inside the chamber. During this movement only the piston post pushes the firing pin forward and the round is fired. (b) Closed Breech Weapons. In these weapons the different components carry the round to chamber and fire the round. When the weapon is cocked the breech block moves forward under the tension of its return spring. During this forward movement it takes the leading round from the magazine and feeds it inside the chamber. After feeding, the breech comes to rest unlike LMG where the round is not fired. Now when the trigger is pressed the firing mechanism is RESTRICTED  RESTRICTED 37 operated and the hammer under the tension of its spring goes and strikes the cap and the round is fired. 13. From the different types of breech mechanism it can be concluded that: (a) In open breech wpns since there is no rd in the chamber, there are no chance of cook off or pre-ignition (due to heated chamber mostly in auto wpns when firing at a very rapid rate). Thus, an open breech ensures/better heat dissipation. (b) Wpns with open breech are less accurate because of the mov of the hy BB and carrier, which causes vibrations and shift in CG. (c) Mech safety is much simpler in the case of open breech than closed breech. In open breech the wpn is designed in such a way that the locking will take place before firing. In closed breech during the fwd motion of the BB (after it has crossed the hammer) if the firer has a quick reflex and presses the trigger, the hammer would get released and strike the firing pin even before the breech is locked. Therefore, addl mech safety devices like the safety sear have to be incorporated which ensures that the wpn is locked before the trigger can be pulled. 14. Safety in 7.62mm LMG. In case of LMG when the trigger is pressed the moving parts move forward. During this move they take the leading round from the magazine and feed it inside the chamber. After some time the round gets fully seated inside the chamber. The breech block completes its forward travel, but piston still has some distance to move forward. During the forward move of the breech block it is lifted up with the help pf piston cam and the locking edges of the breech get locked with the body locking shoulder. Though the locking has taken place still the piston is moving forward and now during the final move of piston the front edge of piston post strikes the firing pin and the round is fired. There is certain amount of play kept between firing pin and piston post. Under no circumstance can the piston-post strike the firing pin before locking has taken place. Because of this the LMG is 100% safe. 15. After the round is fired the bullet moves forward. Once it crosses the gas vent, the gases enter the cylinder and push the piston back and the piston starts moving back. During this rearward movement the breech block slides down and gets unlocked. The time taken by the bullet to travel from gas vent to muzzle is much less than the time taken by breech block to get unlocked. Hence, unlocking does not take place till the pressure in the barrel is safe. 16. Safety in 7.62mm SLR. Mechanical safety in closed breech weapons is not so simple as in open breech weapons. When the moving parts are moving forward, if the firers reaction is fast and he presses the trigger the hammer may strike the firing pin before the locking takes place. To cater for this contingency the safety in SLR is in three parts. (a) Locking. When the carrier and breech block moves forward the breech block takes the leading round of the magazine and feed it and the move of breech block comes to an end. The carrier still has to move a distance of 14mm. RESTRICTED  RESTRICTED 38 The locking ramps in carrier push the breech block down and the locking edges of breech block get locked with the locking shoulders in the trigger housing. This makes the weapon mechanically safe. The only problem now is that if the firer presses the trigger, which is an independent mechanism before the locking takes place the round will get fired when it is not mechanically safe. (b) Safety Sear. To cater for the above eventuality that the firing mechanism is not operated before the locking takes place, the safety sear has been incorporated. When the hammer is cocked, it rotates on its axis. Now in place of trigger sear nose holding the hammer the rear holds the hammer from the upper bent. This makes trigger inoperative. During the final forward movement of the carrier, left rear bottom portion of the carrier presses the safety sear down. This only happens after the locking has taken place. With this the safety sear is forced out of engagement allowing hammer to rotate forward until the lower bent gets engaged with the trigger sear, where it is held until the trigger is placed to release it. This ensures that the trigger is not pressed till such time locking takes place. With this though we have achieved 100% mechanical safety but it is still not fool proof. Say if safety sear breaks again the rifle would not be 100% safe. (c) Shrouding of Firing Pin. To cater for above eventuality the firing pin is so placed that the carrier all the time shrouds the firing pin. It is only exposed when the locking has taken place. At no stage can the hammer contact the firing pin because it is shrouded by the carrier till locking has taken place. This makes the weapon 100% safe. 17. About unlocking, the arrangement is quite similar to 7.62mm LMG. The time taken by bullet to travel from gas vent to muzzle is much less than time taken by carrier to move 14mm i.e. before the unlocking takes place. 18. To sum up the mechanical safety in 7.62mm SLR, the positive locking of breech block takes place before the carrier is fully forward and before the safety sear is tripped by the carrier. The rear end of the firing pin is always shrouded by the carrier except during the final forward movement of the carrier and cannot be therefore struck by the hammer until mechanical lock is completed. 19. How 7.62mm Rifle can be made automatic? (a) The trigger sear of 7.62mm SLR has an oval cavity in it. When the trigger is pressed the trigger sear tail is lifted up and the hammer which has been held at lower bent of trigger sear nose is disengaged. The hammer rotates on its axis and strikes the firing pin. In a normal situation till the trigger is kept pressed the nose should have been kept away from the lower bent. But this does not happen because of the oval cavity in the trigger. Sear is now under the tension of its spring the trigger sear moves forward and again gets in position to hold hammer though trigger is pressed. Now to fire next round the trigger has to be released and then only will the upper step of trigger come under trigger sear tail. (b) To make this weapon automatic all that has to be done is to make this oval RESTRICTED  RESTRICTED 39 cavity round. Because of this cavity being round it will not be able to oscillate forward, as a result the trigger sear nose will at all the time be kept away from lower bent till such time the trigger is kept pressed. Moment the hammer is released by safety sear it will rotate on its axis. As trigger sear will not be there to hold it, it will go and strike the firing pin. This cycle will continue till such time the trigger is released. PART II: OPERATING MECHANISM 20. To study small arms in detail it is necessary to study the ways in which a weapon can be designed to complete the cycle of operation. In this we will first consider the various mechanical principles and functions which in some aspect or aspects are common (general) to all weapons. 21. In all small arms, whatever principle they work on, the store house of power is the chamber. The energy that drives the bullet through the bore is obtained from the chemical energy of the propellant. The propellant, produces a large quantity of gases burning at high temperature and building up an extremely high pressure inside the confines of the volume of the cartridge case held within the chamber. 22. The Chamber. Though there are many types of chambers, but the scope of this study will be kept limited to the tapered chamber, parallel chamber and the fluted chamber. Normally for service pressure ammunition the tapered chamber is used. (a) Tapered chamber. The round in LMG and Rifle is slightly tapered in the front. In a service pressure ammunition because of high pressure the case expands and tightly hugs the chamber walls. If the round is parallel then it will offer resistance all along its length and as a result the extraction will be difficult. To prevent this the chamber is made tapered. In a tapered chamber even if the case slides back by a fraction of a millimetre there will be a gap created between the cartridge case and the chamber walls as a result of which extraction will be simple. (b) Parallel chamber. It is normally used in low pressure ammunition. However, in all the weapons working on the principle of blow back operation, parallel chamber is a must. MP9 and 9mm pistol have parallel chamber. (c) Fluted chamber. This is a recent design. There are longitudinal serrations cut into the chamber which end some distance before the chamber face. When the round is fired the gases lock into these serrations and form a thin film of gases between the chamber and cartridge case. This helps in easy extraction. The serration being not for full length help in obturation thus ensuring safety to the crew. 23. Obturation. When we fire a round, high pressure is generated inside the cartridge case which is held inside the chamber. To use complete pressure to push RESTRICTED  RESTRICTED 40 the bullet forward it has to be ensured that it does not escape from the chamber end. Radially the cartridge case is supported by chamber walls. Though initially there will always be a gap between cartridge case and chamber walls but due to high pressure the cartridge case will expand radially and hug tightly against the chamber walls. This expansion of cartridge case radially will prevent any pressure leaking from the side and back. This is known as obturation. 24. Strong base for cartridge case. In all types of ammunition 1/8th of an inch of the cartridge case base is of solid metal. Rest of the cartridge case is thick at the base and thin on the top (in front side). Except base no other part of cartridge case in strong enough to hold 21 TSI pressure at its own. Even the base also needs support from breech face to contain this pressure. 25. Cartridge Head Space (CHS). CHS is the distance between the front face of the breech block & the point, where the cartridge rests (by resting it means the point which prevents the further forward movement of cartridge case). CHS will be different for rimmed and rimless ammunition. In rimmed arm it is the rim at the base of the cartridge case which prevents it from moving further forward inside the chamber. Hence the CHS will be the distance from the face of the breech block to the rim. 26. For rimless ammunition things become slightly different. Like in case of 7.62 mm rimless ammunition in LMG and rifle it is the small cone of the case that prevents further forward movement. To select a point, take the centre point of small cone in the chamber. Application of CHS is in designing of ammunition to enable mass production. This is a kind of free play kept in the weapon and ammunition design. 27. If CHS is not kept in a weapon i.e. the gap between the breech face and base of cartridge case, the weapon will become a precision weapon. For this precision ammunition would be required. If the ammunition is slightly over sized it will not be fully seated inside the chamber. Hence, the breech will not be able to complete its full forward travel which may prevent the locking of the weapon. Also, if chamber is dirty because of excessive fouling and dirt the locking may not take place. Hence CHS is a must in all types of weapons, except those firing consumable type of cartridge case ammunition. 28. Supporting of case and CHS. When the round is fired, due to pressure the round expands radially and hugs the chamber walls. As there is CHS at the back the round slides back till such time the breech face supports it. How much the round will slide back will depend on the CHS. Hence certain part of the base of cartridge case will be always outside the chamber. The portion which is normally exposed outside the chamber is the solid base of the cartridge. 29. Ruptured case. If the CHS is more than 1/8 of an inch then while firing the case is going to slide back by more than 1/8". As only 1/8” of ca