Topic 9 - Primers and Propellants

Question 1

what are the two MAIN designs of centre fire primers?

Answer 1

BOXER = designed by british army officer Edward Boxer.

BERDAN = designed by US army officer Hiram Berdan

Question 2

what does the anvil do?

Answer 2

the anvil acts as a hard surface for the firing pin to crush the explosive compound against.

Question 3

what does the flash hole do?

Answer 3

the flash hole is where the hot gases created when the primer explodes will enter into the main headspace of the cartridge and ignite the propellant.

Question 4

what is a typical primer charge?

Answer 4

a typical primer charge for centre fire and rim fire primers is LEAD STYPHNATE

Lead 2, 4, 6-trinitrobenzene-1, 3-diolate

Question 5

what is Lead Styphnate

Answer 5

Lead Styphnate is the most widely used initiating compound. this may change to lead-free at some point in the future.

C6 HN3 O8 Pb

a primary high explosive that can be detonated by friction, impact or flame.

not as shock sensitive as mercury fulminate (AK47) or LEAD AZIDE (rim fire), both of which it replaced.

Question 6

what are the properties of lead styphnate

Answer 6

it is relatively heat intensive and does not react with metals. it will not cook off in an overheated firearm. it wont react with the metals of the primer cup or cartridge during storage. it is stable even at high temperatures.

it is highly sensitive to static charge. as low as 0.004J can initiate the detonation. a car static spark can be 0.05J. the friction created by the firing pin impacting the primer cup creates the static. external static is shielded by the brass cartridge case.

detonation velocity = 5200 ms-1

molecular mass = 450.228 gmol-1

Question 7

information about rim fire cartridges?

Answer 7

an earlier development in primer design where the firing pin impacts the rim of the cartridge case.

the primer compound is usually lead styphnate or lead azide is spun into a recess in the case rim.

this system is cheaper to make and its structure means this system is only really suitable for lower energy rounds. almost exclusively used for 0.22” or 5.5mm caliber.

Question 8

what is a propellant?

Answer 8

propellants are energetic materials which deflagrate in a controlled fashion to allow their energy to be used in propelling rockets or projectiles from firearms.

note - deflagrate, not detonate

deflagration is a subsonic commbustion that usually propagates through thermal conductivity - hot burning material heats the next layer of cold material and ignites it.

deflagration is different from detonation, which is supersonic and propagates through shock.

Question 9

what is black powder?

Answer 9

black powder was the first known propellant, its use dating back to at least 424 BC as a pyrotechnic.

it is 14% Sulphur (S)
10% Carbon (C)
76% Potassium Nitrate (KNO3 or saltpetre)

Question 10

what is milled powder?

Answer 10

milled powder was the black powders constituents that were independently ground before carefully being mixed.

Question 11

what is the problem with milled powder?

Answer 11

the separate constituent chemicals of milled powder would settle out during transport and remixing was neccessary prior to use.

this was rather inconvenient in the midst of a battle - slowed the reloading processes even further when muzzle loaded firearms were common.

Question 12

what are some disadvantages of black powder?

Answer 12

shows the enemy where you are firing from because of the smoke clouds

it obscures your own view of what you are aiming at

it clogs the gun barrel - needs cleaning more often

it is hygroscopic - absorbs moisture easily and stops the powder from burning which we dont want

unstable when hot

it is highly sensitive to static

it can produce highly toxic by products

Question 13

what is corned gunpowder?

Answer 13

in 1781, it was found if black powder was dampened and then pressed through a metal screen, the resultant “strings” dried with no separation of the mixture.

“strings” then were ground or “corned” into size

Question 14

how did corned gunpowder aid in steps forward in development?

Answer 14

Corned gunpowder allowed the development
of measured, pre-packaged powder ammunition.

Different sized grains were produced for
different applications.

Question 15

what are the modern propellants?

Answer 15

Modern propellants tend to be classified based on the number of core energetic materials they contain.

Single base contains nitrocellulose (NC).

Double base contains nitrocellulose and nitroglycerine (NG).This is the most common propellant class used in small arms, cannons, mortars and rockets.

Triple base contains NC, NG and nitroguanidine (NGu).

Modern propellants are to as “smokeless”, which is a misnomer, they just produce a lot less smoke than corned powder.

Question 16

what is nitrocellulose? (single base)

Answer 16

Nitrocellulose is six times more energetic than corned gunpowder.

It is created by the reaction between cellulose and nitric acid, before being stabilised by dissolving it in alcohol and ether which when dried allows it to be worked to any shape or grain size safely.

NC is 35% O2 deficient (or has a negative
oxygen balance), meaning that it combusts
to CO instead of CO2 in the absence of
oxygen.

Question 17

what is nitroglycerine? (double base)

Answer 17

Nitroglycerine is highly shock-sensitive and prone to
accidental detonation unless stabilised in ethanol or
acetone. It is more energetic than nitrocellulose.

It has a very efficient combustion process, which
produces almost no smoke at all.

Nitroglycerine has a positive oxygen balance meaning that it does not require oxygen in the air to undergo combustion. The addition of NG therefore helps keep the combustion reaction of NC going inside the cartridge case.

Question 18

what is nitroguanidine?

Answer 18

Nitroguanidine is highly insensitive but energetic high explosive.

It reduces the muzzle flash produced from the propellant as well as the
flame temperature without sacrificing chamber pressure.

Triple base propellants (NC+NG+NGu) are typically used in large bore guns where barrel erosion and flash are particularly common.
* NGu reduces the barrel erosion in firearms.

Question 19

is propellant burning an exothermic or endothermic reaction?

Answer 19

Propellant burning is a highly exothermic reaction, giving out significant quantities of heat.

• Heat is a weapon designer’s worst enemy.

Question 20

what are the several effects of heat build up?

Answer 20

• Barrel distortion - initially leading to poor accuracy and eventually barrel blockage.
• Cook off - where the residual heat present in the chamber prematurely ignites the primer/propellant of the next chambered round.
• Evaporation of lubricants - leading to jamming of the firearm’s action.

Question 21

what are the key variables that effect firearm functionality?

Answer 21

Effective firearm functionality depends on a number of key variables, but the ultimate force (F) applied to the projectile(s) depends on:

Peak chamber pressure (P) and bore cross-sectional area (A).

These variables are related by the following equation

F = P x A

This means that maintaining an optimal chamber pressure is essential to help realise the full potential of the weapon system.

Question 22

why is grain shape crucial?

Answer 22

The surface area to mass ratio is critical to the burn rate of a powder grain.

• The incorrect grain shape/size can cause
  chamber rupture through the generation of
  the incorrect pressure profile for the firearm.
• Smaller, flattened grains burn faster than
  larger, more spherical grains.

Question 23

what are some typical propellant additives?

Answer 23

• Reaction rate modifiers, which change the propellant’s burning rate. * Dinitrotoluene (DNT), carbamate and ‘centralite’ compounds can slow the rate. * Barium nitrate and potassium nitrate can increase the rate.
• Flash reducers, which reduce flash but increase smoke production. * These include potassium nitrate and potassium sulphate.
• Wear reducers, which lower the wear on the inside of the barrel. * These include molybdenum disulphide (MoS2), titanium dioxide (TiO2) & graphite.
• Stabilisers and plasticisers, which help form the propellant grains. * These include resorcinol, diphenylamine and petroleum jelly.
• De-coppering agents, which slow copper build up in the rifling. * These include tin, bismuth and compounds of these metals such as tin dioxide.