Definition Series - Part 6: "Ammunition"
by Kirk Lawson

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Ammunition is to guns as gasoline is to a car. It is a consumable product that is required for the operation of the machine.

There is some slang surrounding the product and we will identify a few of the slang words. We will use the most accurate words here but you should understand that there may be some in the firearms community, who I identify as suffering from "green belt syndrome" [Article - Green Belt Syndrome], who may feel it is their moral duty to correct you if you use a slang term which might better fit for a component. Worry not, we will give you the basics.

The most common type of ammunition for modern firearms is "self-contained, metallic cartridges."

There are four components to a modern metallic cartridge:
  • Case
  • Propellant
  • Primer
  • Projectile
Case: The case is the container that holds all of the components of the metallic cartridge together. Sometimes it is called a "piece of brass" or just "brass" in slang, because brass is the most common material used to make a cartridge case. The case is also often made from steel or aluminum and may be plated with nickel to prevent corrosion and promote smooth feeding.

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[Cases: 9mm Luger, "30-30" Winchester, .308 Winchester]

Propellant: The propellant is what burns rapidly, producing rapidly expanding gasses contained within the case, chamber, and barrel of the gun, forcing the bullet down the barrel and out at high speed. Sometimes the propellant is referred to as "powder," harkening back to the old Black Powder component. Modern smokeless powder is not an explosive. It is a propellant because it does not explode when it burns. It burns fast, but does not explode. When contained in a more-or-less sealed environment, such as within a case inside the chamber of a gun, the rapidly expanding gasses cause pressure which increases the speed at which the "powder" burns, which releases more gasses, which causes more pressure... There is a very delicate and mathematically detailed science behind getting the right propellant, in the right quantities, for a given cartridge. It is exacting and if done wrong creates a very dangerous situation which could lead to injury to the user.

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[Hodgdon brand Titegroup pistol powder]

Primer: The primer is a pressure sensitive compound, usually lead styphnate, which will ignite from a sharp blow. Placed at the rear of a cartridge in modern ammunition, the firing pin strikes the primer, detonating the compound, which sends a tiny jet of flame into the case, igniting the propellant. There are two common types metallic cartridges, differentiated by how the primer is placed. Center-fire cartridges have a pocket at the rear in which a small primer "cap" fits, as a separate and removable component. Rim-fire cartridges, most often .22 Long Rifle, have a rim around the rear circumference of the cartridge which allows for a gap on the inside of the cartridge into which the primer compound is packed a little like sandwich meat between two slices of bread. While the primer is sensitive to a sharp blow it is stable enough that it will not ignite if a cartridge is accidentally dropped.

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[Winchester small rifle primers]

Projectile: This is the heavy bit that is ejected out of the muzzle end at high speed to poke holes in things at a distance. It is proper to call the projectile of most handgun or rifle ammunition a "bullet." Another, older, slang term used is "slug." There are many ways to apply the slang "slug," including to shotgun ammunition (similar to handgun and rifle metallic cartridges) and to a way of measuring the inside of a barrel by driving a piece of soft lead through it. Some people will use the term "bullet" to inaccurately refer to the whole loaded cartridge. While this is not technically correct, if you know what they are talking about then it is not worth correcting them and may cause insult and argument. When you buy ammunition, just call it ammunition or "ammo" for short. If you call it "bullets" the counter guy will know that you are talking about ammo. If he corrects you then just understand that he is either a jerk, or suffering from "green belt syndrome." Ignore the slight and just tell him what cartridges you want.

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[Bullets: 9mm, 9mm epoxy coated, .223 Jacketed Soft Point (JSP), .30 Jacketed Soft Point (JSP)]

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But how do you know what is the right ammunition for your gun or if the ammunition you have is right for a specific gun? The gun itself will be marked with the proper cartridge or "caliber" such as "9mm Luger" or ".40S&W" though there are many more. It should also be listed in your Owners/Users Manual which came with the gun. The ammunition itself will be marked both on the original box and on the base of the cartridge.

While it is beyond the scope of this small article to explore it, you should be aware that some cartridges have multiple synonyms for the exact same thing. This includes 9mm Luger (9mm NATO, 9x19mm), .45ACP (.45 Auto, .45 Auto Colt Pistol), and .380ACP (.380 Auto, 9mm Corto, 9mm Kurtz). Use caution and look it up on a web search if you are unsure.