Ammunition: components, calibre and gauge, malfunctions and storage

Parts of a cartridge

Rifle / handgun cartridge	Shotgun shell
Case - holds everything together (usually brass)	Hull - plastic or paper tube with a brass/steel head
Primer - shock-sensitive compound that ignites the powder	Primer - in the centre of the head
Powder (propellant) - burns rapidly to make gas	Powder
Bullet (projectile)	Wad - separates powder from shot and seals the gas
	Shot (many pellets) or a single slug

Rimfire vs centre-fire

• Rimfire: the priming compound is inside the folded rim of the case; the firing pin strikes the rim (e.g. .22 Long Rifle). Not reloadable.
• Centre-fire: a separate primer sits in the centre of the case head. Used for most rifle, handgun and shotgun ammunition.

Calibre and gauge

• Calibre describes the bore or bullet diameter of rifles and handguns, in hundredths/thousandths of an inch (.22, .308) or millimetres (9 mm, 7.62 mm). The full cartridge name matters: a .308 Winchester and a .30-06 Springfield are both ".30 calibre" but are not interchangeable.
• Gauge describes shotgun bores: the number of lead balls of the bore's diameter that make one pound. The smaller the number, the larger the bore (12 gauge is larger than 20 gauge). The .410 is the exception - it is a bore diameter.

Key fact: Use only ammunition that matches the data stamp on the barrel exactly. If a firearm has no data stamp or you are unsure, do not fire it - have a qualified gunsmith identify it.

Examples of dangerous mix-ups the course warns about:

• A 20-gauge shell can slide into a 12-gauge chamber and lodge in the bore; a 12-gauge shell fired behind it can burst the barrel.
• A .357 Magnum cartridge must not be used in a firearm chambered only for .38 Special (the reverse is generally possible in a .357 revolver, but always follow the manufacturer).