Key firearm and ammunition terminology Flashcards
The firing process
- The primer is activated by the impact from the firing pin
- Propellant starts to burn due to heat from the flash hole, gas and pressure are produced and the cartridge expands
- Once pressure is sufficient the bullet is fired from the cartridge and it is launched down the barrel and the propellant continues to burn
Described angle
Angle between the longtiudinal bullet axis (straight line up the bullet) and the inscribed rifling marls
Producing rifling
Standard (rectangular) profile:
* Broach-cut: uses a single point tool to cut one groove at a time
* Electro-chemical etching: uses an electrolyte, which is passed through grooves in a tool whilst in contact wiht the inside of the barrel to etch away the material and form the barrel grooves
Polygonal rifling:
* Hammer-forged: a mandrel with the rifling profile machined into it is inserted into an oversized barrel, which is then hammer forged onto it to form the barrel grooves
* Button-formed: button with the rifling profile machined into it being forced through the barrel to form the grooves
Self-loading pistol: Semi-automatic mechanism
- Pulling back of the slide allows the ammunition in the magazine to present itself to the rear of the barrel
- Moving the slide forward under spring pressure, the round is pushed from the magazine into the chamber of the barrel
- The action cocks the trigger mechanism
- Pull the trigger, hammer drops and the round is fired
Bolt-action mechanism - rifles
- Pushing the bolt forward brings the bolt face into battery with the breech end of the barrel and cocks the firing pin
Self-loading rifles mechanism
- If it is short recoil it will operate as a normal self-loading pistol
- If it is long recoil, after reaching the end of its travel the barrel is unlocked and pushed forward by spring action ejecting the spent cartridge during its forward motion, when the barrel is fully forward, the breech block behind its forward motion reloads a fresh cartridge into the chamber and cocks the action
Pump action rifles mechanism
- On pulling back the fore-end, the mechanism locking breech block to the barrel is released
- By pulling the fore-end to the rearmost extent of its travel then pushing it forward, the empty cartridge case is ejected and a fresh round is loaded into the chamber and the action is cocked
Self-loading definition
A repeating firearm requiring a separate pull of the trigger for each shot fired. After manually loading the first round from the magazine, the weapon will use the energy of discharge to eject the fired cartridge and load a new cartridge from the magazine into the barrel ready for firing
What must the primer cup in centre fire ammunition be like and why?
- Must be soft enough to be crushed by the firing pin
- This means the cartridge case could be made of stronger material which would act as a gas seal for much higher pressure than could be obtained with rim-fire ammuniton
What is rimfire and centrefire in terms of the primer?
- Rimfire: self-contained cartridge with the priming compound held in the hollow base rim
- Centrefire: ammunition with the priming compound held in the cap in the centre of the base of the cartridge case
Single shot mechanism - not for pistols
- On unlocking, the barrel swings down allowing the empty cartridge case to be removed and a fresh one to be inserted
Single vs double action revolving pistol mechanism
- Single: cocking the hammer rotates the cylinder via a ratchet mechanism to bring a new round of ammunition in line with the barrel, pulling the trigger then drops the hammer thus firing the round
- Double: a long continuous pull on the trigger cocks the hammer, rotates the cylinder then drops the hammer all in one operation
What is a disconnector?
- Disconnects the trigger from the rest of the system in self loading pistols so that it doesnt continue to fire
How do you measure the headspace and what is it?
- The headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge to the face of the bolt
- With rimfire the headspace is measured from the bottom of the rim to the top of the rim
- With centrefire the headspace is from the bottom of the cartridge to the neck or the end of the cartridge
What is a partitioned bullet?
- Rather than a single lead slug shaped into a bullet, the partition is two separate lead components separated by a partition
