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What Are The Basic Parts Of Ammunition?

What Are The Basic Parts Of Ammunition?
December 14, 2022 Edited February 2, 2023 336 view(s)
What Are The Basic Parts Of Ammunition?

Ammunition (or as my redneck self calls it) ammo, has never been in more demand. I take that back… during the height of the recent Covid Catastrophe you couldn’t find ammo. But, even though it’s back, it still isn’t to the level it was pre-Covid and the price is up. What’s this got to do with the parts of ammo, you ask? Not a whole lot, other than the fact that ammo (or lack of it) has been at the forefront of shooting sports for over two years. In this respect, it might help if we looked at the various components. It might help us to understand why ammo has been so scarce. So, let’s take a look!


Ammo Types

Before we jump off the ammo cliff, let’s take a quick peek at the different types of ammo that we can buy. There are three main categories…




All three of these ammo types consist of four main components…

case (or shell, for shotguns)

  • primer (or priming compound, rimfire)
  • powder
  • bullet (or shot load/slug, again for shotguns)

Everything that you can stuff into your gun’s chamber has these four items in common.

Centerfire and rimfire cartridge parts diagram.

How they put them together may vary, but they all work pretty much the same way. I’ll provide a few pics from my reloading area (all non-credited photos are mine). I’m not fancy, but I get the job done. Being a reloader in these times is a good thing! 

basic parts of ammunition graphic


The Parts of Ammo

Let’s look at the four components of ammo and examine each one’s purpose.

Bowl full of empty 9mm shell casings



This is the thing that holds it all together. The centerfire cartridge case (official name) is made of a brass, steel, or aluminum alloy. There have been other types, but these are top three. Rimfire cases are almost always brass, and shotgun shells in the olden days were paper but more recently, plastic has taken over as it is not affected by weather and is tougher. Cases may be plated or otherwise externally changed but they are the same underneath.w

Cases have one thing in common… a primer pocket and flash hole that allows the primer’s spark to ignite the powder. I won’t go into Berdan vs. Boxer priming, etc. … just understand that without a flash hole, you won’t have a “bang!” Check out our guide to Steel vs. Brass Ammo if you want to learn more.


Musings About Cartridge Cases and Reloading

Cases vary, of course. A centerfire rifle case will most often have a shoulder that stops the cartridge’s forward progress into the gun’s chamber. That’s called headspace. Rimmed cases for revolvers and some rifles headspace on their rim. Cases for rimfire calibers do not have a primer hole but carry their priming compound in the rim. That’s why you see a little rectangle-shaped dent in the rim of a .22 LR after you fire it… that’s where the firing pin hits, and also why you shouldn’t dry-fire .22s without a snap cap of some kind. You can damage the chamber and/or the firing pin.

Cases are typically pretty tough customers. They have to be, in order to contain the prodigious pressures that are generated by even the lowliest of the ammo classes. They tend to last a long time – being a reloader for almost 50 years I can vouch for that. Brass cases have to be made to high specs, and must be made of the proper alloy. I do believe this was why ammo was so hard to find a year or two ago – raw materials for cases (and bullets, for that matter) wasn’t able to be moved so we had shortages.

There are two main reasons that you may not be able to reuse a brass case for reloading. The first is if it developed a split, either at the case mouth (most common) or lower down (this is not as common. Usually, if this happens, the thing exploded and probably sent pieces of the gun hurtling skyward. I’ve had that happen, as I’m sure many of you have, too). The second reason that you won’t be able to use a case for reloading is if you lost it when your semi-auto kicked it out into the next zip code. That is way more common than reason #1. That’s one reason I like revolvers. I know, I know… I’m old school. What can I say?

Rimfire cases are rimmed and carry their priming compound in the rim. They tend to be less reliable than centerfire cartridges for that reason. How many times have you pulled the trigger on a .22LR, only to have it go “thunk” instead of “bang”? Sometimes, just rotating the little .22 round in the chamber a little will expose a good section of priming compound and then it will fire, but we usually don’t want to mess with that, do we?

As for shotgun shells, they are pretty straight-forward. They usually carry a 209 primer in their base, and have a section of brass (either low or high) at the base to impart strength. The rest of the case is usually plastic nowadays which is plenty to contain the relatively low pressures that these shells typically produce.

That’s enough about cases. Let’s move on!

Box full of primers for making ammunition.



Primers are the spark plugs of the cartridge world. Without the spark, or flame they produce nothing would happen when you pull the trigger. They are vicious little poppers… don’t ever set one down and hit it with a hammer! There’s enough “oomph” produced by primers that they are enough, all on their own, to propel plastic or wax bullets at a decent velocity. 

Primers for centerfire cartridge reloading come in two flavors… regular and magnum. The magnum number is juiced a little more to make a hotter flame. Some slow-burning powders that can fill the case require a pretty good flame to get ignited and the magnum primer does that. I reload mostly for handguns, and target loads at that so I don’t need magnum primers.

During the Covid times, primers were the hitch in the git-along that reloaders ran into. You could pretty much find bullets and even some powders, but without primers, it didn’t matter. We wrote an article about a year ago about the ammo shortage, check it out if you're interested! 


Shotgun shell loader

About the only thing you need to remember about primers aside from not hitting them with hammers is to store them in a dry, cool area and not contaminate them. If you have any lube at all on your fingers – case lube, oil, some solvents – you can deactivate them if it gets into the cup. So, keep the area clean and your primers will be happy.

Fridge full of powder for making ammunition.

(Yup, you’re right – that’s a refrigerator. I keep my powder in a garage fridge because exposure to heat can degrade powders over time. Here’s a good article on why I store powder in the fridge).



We’re talking about smokeless powder here, not black powder… that’s a different critter. Smokeless powder (I’ll drop the “smokeless” from now on – you know which one I’m talking about) can be fast, medium or slow in terms of burn rates. There are burn rate charts that list all powders from slowest to fastest. What do I mean? A fast powder burns very quickly and is typically used in revolver or pistol target applications, where you don’t need a whole lot of velocity. These powders tend to be more economical to use since you don’t need as much of them in the case as opposed to a slow powder. They are also easier to ignite than slow powders.

Slow powders are used where maximum velocity is needed. These powders tend to fill the case, as you will use a lot more of a slow powder than a fast one. They also tend to need magnum primers to ignite them. Since this is not a treatise on gunpowder, let’s leave it there.

I just need to say one more thing, in case any of you are inspired to go out and buy reloading equipment and components. Be careful with fast powders. It is really easy to double-charge a pistol case with, say, 8 grains of Bulleye when you wanted only 4. That can be a recipe for disaster – I know. This rarely happens with slow powders since they tend to come closer to filling the case. A double charge would spill powder all over the bench. It CAN be done, but it’s harder.

On to the thingy that comes out the end of the barrel - the bullet.

Bucket full of bullets Bucket full of ammunition



Above you see two products of another of my hobbies, bullet casting. Here we have a powder-coated 124-grain 9mm bullet (L) and a 160-grain .357 SWC (R). Both are from Lee molds. This is one type of bullet, but if you shoot many autoloaders, you’re probably not too familiar with cast bullets. You are more likely to shoot jacketed bullets – either full-metal jacket (FMJ) or hollow-point (JHP). Nothing wrong with either of these except the fact that I can’t make them in my garage like I can the others. Again, as with powders, this is not an essay on bullet types and manufacture, so we’ll cut to the chase.

If you shoot only store-bought ammo, you’re good to go. Most commercial ammo is very good – it’s reliable, accurate, and is becoming less expensive in these post-crazy times. If you are wanting to expand your shooting hobby, reloading is the next logical step.

Please note that the bullet is what comes out of the barrel. The cartridge is what you load into your magazine and consists of the four parts that we are discussing herein and should not be called a bullet. That is equal to calling a magazine a clip – read about that in our article about clips vs magazines. There’s nothing snobbish about using correct terminology… it’s just that more shooters will understand what you are referring to if you use the right words. Anyway, that’s about it for bullets.


Summing Up

We’ve touched on the four components of modern ammo. As with other collections of parts such as your daily driver, if one part fails the whole thing is bupkis and you chance going nowhere.

If the primer fails, that’s not a huge deal – nothing happens. But if a case fails, fireworks can ensue. I’ve blown guns up when the cartridge case let go – that ain’t my idea of a good time, trust me.

It takes all four parts of a cartridge to have it go “bang”, and when it does, isn’t the fun part? If you have any questions or comments, below is your area to leave them. Now - let’s get out and go shootin’!


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