Explosives and Propellants

• Explosives store chemical energy and release it quickly to perform ordnance functions like propelling projectiles or exploding warheads.
• Explosives are categorized as propellants or high explosives, differentiated by their burning or detonating rates.
• Propellants burn at a high, reproducible rate, below detonation speed, whereas high explosives function through detonation.
• Propellants can detonate and high explosives can burn under certain conditions, but their intended use is what sets them apart.

Propellants

• The propellant is the active component of the propelling charge inside a cartridge case.
• A primer initiates the burning of the propellant.
• The primer contains a small amount of igniter material.
• Propellant burns at a high, reproducible rate, generating a large gas volume, which builds pressure and propels the projectile.
• Gunpowder's invention is credited to Friar Francis Bacon, though Chinese legends suggest earlier use.
• Early gunpowder was charcoal, sulfur, and potassium nitrate.
• Modern black powder is 75% potassium nitrate, 15% charcoal, and 10% sulfur.
• Until the late 1880s, black powder was the primary gun propellant.

Black Powder

• Black powder is susceptible to moisture, causing deterioration and unpredictable performance.
• Dry black powder maintains its properties almost indefinitely.
• Black powder necessitates frequent gun cleaning because of its residue.
• It also causes barrel erosion.
• Black powder produces vast amounts of smoke and has low ballistic reproducibility.
• Black powder is sensitive to friction, sparks, and heat.
• Nitrocellulose (NC) was first created in 1838.
• NC is a fibrous white powder.
• NC burns cleanly with little smoke and is safer to handle than black powder.
• NC colloided with alcohol and ether in 1886 by Vieille, creating a denser, controllable material.
• This was the first smokeless powder, which resulted in new gun propellants.
• Further advancements included stabilizers, flash suppressants, additives for hygroscopicity reduction, and flame temperature reduction.
• Nitrocellulose (NC) remains the basis for almost every gun propellant used today.

Smokeless Powder

• Smokeless powder is used to propel charges for gun ammunition.
• It is typically in the form of right circular cylinders with zero, one, or seven perforations.
• Smaller calibers use slightly flattened balls called Ball Powder®.
• The shape/granulation controls the propellant's burning surface area, it also controls gas generation and pressurization.
• Smokeless powder formulations are primarily colloided NC with a stabilizer like diphenylamine, 2-nitrodiphenylamine, ethyl centralite, or akardite.
• Stabilizers prevent the decomposition of NC from accelerating, interrupting by reacting with initial products.
• Stabilizer depletion depends on temperature and humidity, with high levels speeding up decomposition.
• Surveillance testing predicts the safe handling life of the propellant.

Classification of Smokeless Powder

• Single-base, double-base, and triple-base smokeless powders exist
• Single-base powder mainly comprises NC with a stabilizer and is prevalent in the Navy inventory
• Single-base powder grains are hard, translucent off-white and may have a graphite coating for improved loading
• The color of single-base grains darkens with age but doesn't indicate any loss of stability/performance
• Double-base powder, used only in small-caliber ammunition, consists of NC plasticized with nitroglycerin (NG)
• Double-base powder increases the propellant's energy and toughness
• Double-base powder may be small seven-perforated grains or Ball Powder® coated with graphite for a dark gray surface
• Triple-base powder is made of NC, NG, and nitroguanidine (NQ)
• NQ is a white, crystalline solid that increases the energy density and lowers the propellant's flame temperature

Type/Index Number of Smokeless Powder

• Each lot of propellant for large caliber ammunition has a type/index number (see Appendix D)
• Class designation letters indicate chemical components of the powder:
  • SP - Smokeless powder
  • B - Blended
  • C - Stabilized by EC
  • D - Stabilized by diphenylamine
  • F - Flashless
  • G - Includes nitroglycerin and nitroguanidine
  • N - Nonhygroscopic
  • W - Reworked by grinding
  • X - Water-drying process
• Following letters indicate the sequence of lot acceptance.
• Powder already loaded into ammunition doesn't have a type/index number.
  • SPC - Cool burning, single-base powder (SP), nitrocellulose, with ethyl centralite (EC) as a stabilizer (also known as carbamite)
  • SPCF - Single-base powder similar to SPC with a flash suppressor (F) of potassium sulfate. BS-NACO propellant is the primary example
  • SPCG - Cool burning, triple base powder commonly referred to as "Cordite N", stabilized by EC, contains nitroguanidine, nitrocellulose, and nitroglycerin. It is a flashless powder, though the letter “F” is not used.
  • SPD - Single-base powder (SP), stabilized with diphenylamine (D). Pyrocellulose or Pyro is the prime example
  • SPDB - Diphenylamine-stabilized smokeless powders (SPD) that have been blended (B). Used to provide a uniform type/index of similar size and performance from smaller lots.
  • SPDE - Experimental powder containing lead carbonite for decoppering purposes; otherwise similar to SPD powder
  • SPDF - Diphenylamine-stabilized smokeless powder (SPD) including potassium sulfate (F) as a flash suppressant. Propellant with flash suppressant in its formulation performs better causing the salt pellets to leave a residue, necessitating more frequent inspections and cleaning when rounds incorporating them have been fired..
  • SPDN - Diphenylamine-stabilized smokeless powder (SPD) with dinitrotoluene to reduce hygroscopicity (N), making it nonhygroscopic, and is often referred to as NH.
  • SPDW - Diphenylamine-stabilized smokeless powder (SPD) reworked (W) by grinding and stabilizer addition, often used for target practice/reduced charges.
  • SPDX - Diphenylamine-stabilized smokeless powder (SPD) water dried (X) in heated water tanks to remove volatile solvents and then air-dried.

Black Powder

• Black powder is still used as igniters, expelling charges, a delay element, a magazine element in fuzes, and a noisemaker.

• It is loaded into primer tubes for cased charges.

• It has a burn rate that is nearly independent of pressure.

• The appearance of black powder is adequately described by its name.

• Finer granulation leads to more rapid pressure development.

• Various granulations are used in gun ammunition components like fuzes, saluting charges, primers, and expelling charges

• Granulation sizes are now designated by class (using U.S. standard sieves):

• GRADE (OLD SYSTEM) / CLASS (NEW SYSTEM)

  • Cannon / 2
  • Musket / 4
  • FFG / 4
  • Shell / 6
  • FFFG / 6
  • Fuze / 7
  • FFFFG / 7
  • Meal / 8

Grain Geometry

• Burning characteristics, pressure, and surface area are what determine the rate at which gas is produced.
• Larger grains have less surface area but generate less gas, and pressure rises more slowly.
• Grains with more perforations yield faster pressure rises.
• Grain size and shape must match the gun performance.
• Overpressurization results from small grains generating gas too quickly.
• Large grains yield less than optimal performance since it may not burn completely.
• Grain size is discussed in terms of the web.

Interior Ballistics

• Interior ballistics encompasses phenomena inside the gun from primer initiation to projectile exit.
• It includes flame spread, pressure rise, and subsequent decrease.
• The pressure-time curve is an important tool.
• Designers optimize the curve for efficient, reproducible, and safe performance.

Composite Propellant

• It is used in rocket motors for thrust.
• It consists of a binder (HTPB), an oxidizer (Ammonium Perchlorate (AP)), a metal fuel (aluminum), and burn-rate modifiers.
• Composite propellant is cast directly into rocket motors and cures into a solid.

High Explosives

• High explosives release energy rapidly.
• This release creates high temperatures, large gas volumes, and high pressures.
• Military high explosives are chemical compounds that decompose extremely fast.
• A "detonation" is approximately 7,000 meters per second generating gas, heat, noise, and a shattering effect.
• High explosives usually include nitrated products of organic compounds or compounded from heavy metals.
• A high explosive can be a pure compound or an intimate mixture.

Classification of High Explosives

• Primary explosives are sensitive and easily initiated by heat, impact, or friction.
• Primary explosives invariably react to stimulus by detonating, unlike simple burning.
• Primary explosives have a sensitivity and are used to initiate more powerful booster explosives.
• Secondary explosives include booster and main charge explosives.
• Secondary explosives are less sensitive than primary explosives.

Use in Gun Ammunition

• All gun ammunition, 20mm or larger, contains a high explosive burster (main) charge detonated at the target.
• Navy gun ammunition consists of a fuze, sometimes an auxiliary detonating (AD) fuze, and a main charge.
• The fuze (including the AD fuze) contains one or more detonators, one or more leads, and a booster.
• The arrangement of components in a projectile is called an explosive train.
• A typical explosive train is a detonator, a lead, a booster, and a main charge.
• The detonator is initiated either by a firing pin or by electric current through a wire.
• The lead amplifies the detonation shock wave and transfers it to the booster.

Detonators

• Detonators, used in fuzes or AD fuzes, contain primary explosives.
• They are misaligned with the explosive train during production/handling/storage until gun firing.
• Surrounding hardware contains the detonator's output in case of accidental initiation.
• Gun firing aligns the detonator with other elements after the projectile leaves the gun.

Description of Detonators

• Detonators, whether stab or electrically initiated, are composed of initial, intermediate, and base charges.
• The initial charge is activated by mechanical/electrical heat.
• Transition from burning to detonation takes place in the intermediate charge.
• The base charge intensifies the shock.

Leads and Boosters

• Leads and boosters transmit and augment the detonation established by the detonator.
• Booster explosives are more sensitive than main charge explosives but less sensitive than primary explosives.

Burster or Main Charge Explosives

• The main/burster charge fragments the case and destroys or damages a target.
• It is selected for safety, performance, and cost.
• Navy gun ammunition uses press-loaded explosive powders.
• The 5-inch gun ammunition uses Composition A-3.
• The current 76mm projectiles are loaded with composition A-3 as well but the latest design replaces it with Plastic-Bonded Explosive.
• 20MM ammunition is loaded with tetryl.
• Pressed comp A-3,5-inch, 54 caliber HI-FRAG round, and the more recent 5-inch, 54 caliber MK 64 designs are loaded with Cast-cured plastic-bonded explosive. PBXN-106. The most recent 5- inch, 54 caliber MK 64 design replaces PBXN-106 with PBXN-9, a pressed plastic-bonded explosive.