Primers and propellants

Question 1

Centre-fire primers: Boxer and Berdan

Also state what a flash hole is and what an anvil does

Answer 1

Boxer
* One flash hole
* Anvil is inside the primer cup (internal anvil)
Berdan
* Two flash holes
* Anvil is part if the cartridge case
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.
The anvil acts as a hard surface for the firing pin to crush the explosive compound against.

Question 2

Lead Styphnate

Answer 2

• Typical primer charge for centre-fire and rim-fire primers
• Heat insensitive and does not react with metals
• Highly sensitive to static change

Question 3

Propellant

Answer 3

• Energetic materials which deflagrate (burn) in a controlled fashion to allow their energy to be used in propelling rockets or projectiles from firearm

Question 4

Deflagration

Answer 4

A subsonic combustion that usually propagates through thermal conductivity - hot burning material heats the next layer of cold material and ignites it

Question 5

Black powder

Answer 5

• First known propellant
• made up of sulfur, carbon and potassium nitrate
• The separate consituent chemicals would settle out during transport and remixing was necessary prior to use (consituents were independently ground before being mixed - milled powder)
• Created a lot of smoke - shows enemies where you are, obscures your view, clogs gun barrel so needs regular cleaning
• Unstable when hot
• Highly sensitive to static (unexpected ignitions were common)
• Produced highly toxic by-products
• Hygroscopic (absorbs moisture to stop it from burning)

Question 6

Corned gunpowder

Answer 6

• Black powder that is dampended and pressed through a metal screen, the resultant strings dried with no separation of the mixture, strings were then ground to the required size
• Can produce different sized grains for different applications
  *1. Larger grains would burn more slowly but release more energy - good for larger weapon systems
  2. Smaller grains would burn quickly and release energy more rapidly - good for smaller weapon systems

Question 7

Modern propellants

Answer 7

Nitrocellulose
* Single base
* Created by the reaction bewteen cellulose and nitric acid
* More energetic than corned gunpowder
Nitroglycerine
* Double base
* Produces almost no smoke (very efficient combustion process)
* Prone to accidential detonation
* More energetic than nitrocellulose
* Has a positive oxygen balance - doesnt require oxygen to undergo combustion

Question 8

Grain size and shape

Answer 8

• Smaller, flatterned grains burn faster than larger, more spherical grains
• Toroidal (doughnut-shaped) and hallow cylindrical grains gives the highest burn rates
• Small, fast-burning grains are used in the cartridges of pistols and short barrelled firearms
• Larger, slower-burning grains are used in rifle ammunition

Question 9

Propellant additives

Answer 9

• Reaction rate modifers (change the propellants burning rate)
• Flash reducers (reduces flash but increase smoke production)
• Wear reducers ( lowers the wear on the inside of the barrel)
• Stabilisers and plasticisers (helps form the propellant grains)
• De-coppering agents (slow copper build up in the rifling)