Topic 9 - Primers and Propellants Flashcards
What are the two main types of centre-fire primers?
- Boxer, designed by British Army Officer Edward Boxer
- Berdan, designed by US Army Officer Hiram Berdan
What does the anvil do?
The anvil acts as a hard surface for the firing pin to crush the explosive compound against
What happens in the flash hole?
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.
What is a typical primer charge for centre-fire and rim-fire primers?
- Lead Styphnate
- C6HN3O8Pb
What did Lead Styphnate replace?
- Mercury fulminate
- Lead azide
- LS isn’t as shock-sensitive
What are the properties of lead styphnate?
Heat insensitive, cook-off, static charge
- Relatively heat insensitive and does not react with metals.
- Will not “cook off” in an overheated firearm.
- Won’t react with the metals of the primer cup or cartridge during storage.
- It is therefore stable in storage, even at high temperature.
- Highly sensitive to static charge.
- As low as 0.004 J can initiate the detonation.
- A car static spark can be 0.05 J.
- The friction created by the firing pin impacting the primer cup creates the static.
- External static is shielded by the brass cartridge case
What is a rim-fire cartridge?
- Where the firng pin impacts the rim of the cartridge case.
- Cheaper to make
- Structure means its only suitable for lower energy rounds
- Almost exclusively used for 0.22” or 5.5mm caliber
What are propellants?
Deflagrate
Propellants are…“energetic materials which deflagrate in a controlled fashion to allow their energy to be used in propelling rockets or projectiles from
firearms.”
What is deflagration?
Subsonic combustion
Deflagration is a subsonic combustion that usually propagates through thermal conductivity - hot burning material heats the next layer of cold material and ignites it.
What was the first known propellant and what is it made up of?
- Black powder
- 14% Sulfur, 10% Carbon, 76% Potassium Nitrate
What was wrong with the first propellant?
Burned residues, combustion process
- The separate constituent chemicals would settle out during transport and remixing was necessary prior to use.
- Slowed reload process.
- The combustion process is not particularly efficient
- Produces lots of partially burned resides that get released through the barrel.
What were the main probless caused by the resulting smoke of black powder?
- It shows the enemy where you are firing from.
- It obscures your own view of what you are aiming at.
- It clogs the gun barrel, making it necessary to stop for regular cleaning.
What are more disadvantages of black powder?
Unexpected ignition, by-products, combustion residues
- It is hygroscopic.
- It is unstable when hot.
- It therefore has a low “cook off” temperature.
- It is highly sensitive to static.
- In a pre-cartridge era, unexpected ignitions were common.
- It can produce highly toxic by-products.
- Depending on the conditions, it can produce combustion residues of sulphuric acid which corrodes weapon barrels as well as being a major health hazard.
What did corned gunpowder allow?
The development of measured, pre-packaged powder ammunition
What are the different types of modern propellants and how are they classified?
Nc, Ng, NGu
- 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).
- Other additives are also added to the propellant mixes
What are the features of nitroglycerine?
Shock, energetic, combustion
- Highly shock-sensitive so 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.
What are the features of nitroguanidine?
Insensitive, energetic, muzzle flash, propellants, barrel
- 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 barrel erosion in firearms.
What reaction is the burning of propellant?
Highly exothermic, gives out significant quantities of heat.
What can lead build-up from the burning of propellant cause?
Distortion, cook-off, exaporation, failure
- 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.
All of the above can lead to destructive failure with the possibility of death or major injury.
What does the ultimate force applied to a projectile depend on?
- Peak chamber pressure (P)
- Bore cross-sectional area (A)
What is maintaining an optimal chamber pressure optimal for?
Maintaining an optimal chamber pressure is essential to help realise the full potential of the weapon system.
How can you affect pressure creation?
Size, volume, additives
Pressure creation is controlled via the propellants properties:
* Grain size and shape
* Volume of propellant
* Grain packing density
* Chemical additives
What is the surface-to-mass ratio of a grain critical for?
The surface area to mass ratio is critical to the burn rate of a powder grain.
What do smaller, flatter grains do?
Smaller, flattened grains burn faster than larger, more spherical grains.
What do toroidal (doughnut-shaped) and hollow grains give?
The highest burn rate
When are small, fast-burning grains used?
Small, fast-burning grains are used in the cartridges of pistols and short barrelled firearms
When are larger, slower-burning grains used?
Larger, slower-burning grains are used in the
cartridges of rifle ammunition.
What can incorrect grain size/shape lead to?
The incorrect grain shape/size can cause chamber rupture through the generation of the incorrect pressure profile for the firearm.
What are the different types of propellant additives?
- Reaction rate modifiers
- Flash reducers
- Wear reducers
- Stabilisers and plasticisers
- De-coppering agents
What do reaction rate modifiers do?
- 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.
What do flash reducers do?
- Reduce flash but increase smoke production.
- These include potassium nitrate and potassium sulphate.
What do wear reducers do?
- Lower the wear on the inside of the barrel.
- These include molybdenum disulphide (MoS2), titanium dioxide (TiO2) & graphite
What do stabilisers and plasticisers do?
- Help form the propellant grains.
- These include resorcinol, diphenylamine and petroleum jelly
What do de-coppering agents do?
- Slow copper build-up in the rifling.
- These include tin, bismuth and compounds of these metals such as tin dioxide.
Boxer centre-fire
- Designed by British Army officer Edward Boxer
- 1 flash hole
- Cup
Berdan centre fire primers
- designed by US Army officer Hiram Berdan
- 2 flash holes
- cup
- Anvil
Rim-fire cartridges
- Firing pin impacts the rim of the cartridge
- 0.22” or 5.5mm caliber
- Cheaper to make
Milled powder
Initially, black powder’s constituents were
independently ground before being carefully
mixed.
Corned gunpowder
- In 1781, it was discovered that if the black
powder mixture was dampened and then pressed through a metal screen, the resultant strings dried with no separation of the mixture - The “strings” were then carefully ground (or
‘corned’) into the required size.
Corned gunpowder allowed
Corned gunpowder allowed the development
of measured, pre-packaged powder
ammunition.
