Table of Contents

Ammunition or Ammo is a package of various components that, when combined, act to propel a projectile from a rifle, gun or weapon.  The word ‘ammunition’ comes from the French term ‘la munition’, which meant equipment or stores used in war.

Cartridge or Shell Casing

A cartridge or shell casing, is simply a container for the propellant which is used to “propel” the projectile or bullet. While the cartridge or shell casing can be a term equally applied to large artillery guns, we will limit the conversation to small arms on this site.

Around the late 1500’s the first cartridges appeared. These were gunpowder wrapped in paper packages which was then thrust down the barrel followed separately by the projectile, typically a ball of metal.

Later, in the 1800’s, cartridges were made of other materials which enabled the cartridge to incorporated the propellant and projectile into one unit.

paper cartridge
A paper cartridge

Projectile or Bullet

22 caliber bullet
Berger .22 Caliber 52 Grain Target Bullet
Berger 6.5mm 140 Grain Hunting Bullet
Berger 6.5mm 140 Grain Hunting Bullet
33109 338 Caliber 300 Grain Hybrid OTM Tactical
Berger .338 300 Grain Bullet

A projectile or more commonly bullet, is the object given kinetic energy by the propellant. Usually tapered for better aerodynamics, bullets are made of many materials but usually lead.

Bullets are sized in terms of weight and diameter or caliber as it is known.

Bullet weight (or mass) is measured in grains ¹ and equates to 64.79891 milligrams.

Diameter is measured both in metric and imperial and is the measurement in the barrel from land to land. See Caliber.

For example:

5.56mm 3.56 gram caliber (NATO) cartridge = .223  55 grain cartridge


A propellant is what imparts it’s energy to the projectile to force it down the barrel. Early in firearm development the propellant was black gunpowder progressing to modern day nitroglycerin or nitrocellulose based compounds.

While it seems like an instantaneous explosion to us, the chemical reaction that occurs is in fact a “burn”. Different burn rates are dictated by the powder grain size ² and shape.

The burn rate regulates the amount of “pressure”, measured in CUP ³ or PSI, that is exerted on the projectile which in turn contributes to the velocity imparted to the bullet leaving the muzzle.

Short barrels such as pistols require a quick burn propellant to build pressure behind the projectile in the limited barrel length. Whereas rifles with their longer barrels can have a slower burning propellant.

Australian Munitions Manufacturing
Australian Munitions Manufacturing

Primer or Fuse

Sellier and Bellot Primers
Sellier and Bellot Primers
Winchester Primers

A Primer or Fuse is the method of igniting the propellant. Early black gunpowder muskets had a touch hole in the barrel which exposed the powder directly to a lit fuse applied to it.

Slow and cumbersome, this was replaced by fine powder piled onto a flash pan which in turn was connected to the barrel through a flash hole. When the powder on the pad was ignited by sparks, for example from a piece of steel struck by flint (flintlock), the hole activates the internal powder charge.

It wasn’t until the early 1800’s with the invention of the percussion cap, that the propellant became protected from external elements.

Today we use primers, which are an evolved version of the percussion cap. Shock sensitive chemicals are used, typically in a small capsule (centrefire) or crimped into the cartridge case rim (rimfire), to ignite the propellant. 


  1. Grain is an antiquated term used measuring the mass of an object. Based on the mass of an ideal seed of cereal such as wheat.
  2. Grain Size is the diameter of individual particles of sediment or powder in the case of ammunition.
  3. CUP or Copper Units of Pressure is a term applied to the estimation of chamber pressures in firearms. PSI is now readily instead used although the use of CUP is still common.

Photo Credits: Mykola Makhlai | Unsplash.

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