If you’re a beginner in guns, bullets and ammunition, there’s a lot to learn– so much that it can easily become overwhelming for novices.

Let’s get down to the basics! Check out our beginner’s guide to bullets and ammunition where we’ll introduce you to a few different concepts here:

• Bullet Size and Caliber
• Rimfire vs Centerfire
• Common Calibers
• Common Bullet Types

Let’s get started!

Bullet Size and Caliber

When it comes to guns and bullets, the first thing to know is “caliber” or the gun’s barrel diameter – and therefore the diameter of its bullet.

For the sake of getting familiar with gun terminology, you should also understand that a “bullet” is just the metal projectile. The entire item (which includes the casing, powder, and primer) is called a “cartridge.”

With the terminology out of the way, let’s look at the next topic.

Rimfire vs. Centerfire

The first way different cartridges are differentiated between is by the placement of the primer – whether it’s a rimfire cartridge or a centerfire cartridge.

Rimfire cartridges have their primer built into the casing’s rim, whereas centerfire cartridge primers are placed in the center (hence their names – easy to remember).

The .22R is the most common of the rimfire cartridges, which are also typically a lot cheaper than centerfire cartridges. You can easily pick up rimfire cartridges for a few cents each.

Centerfire cartridges are further split into two sub-categories: those with a boxer primer and those with a Berdan primer.

Take a look at the below graphic to see the differences:

Common Calibers

There are a LOT of different calibers available. However, as a general rule, you won’t come across more than a handful of them. For this reason, we’re going to focus on the most common.

To add to the confusion, some calibers are given in inches, while others are given in millimeters. You might also come across talk of “grain,” which is a really minuscule measure of unit about 1/7,000th of a pound. And when you get to a higher level of bullet conversation, you’ll start hearing about “stopping power.”

Stopping power is a somewhat vague and controversial trait. It essentially describes how many bullets are needed to drop a person. As you can imagine, that’s what makes it so vague – different people require different stopping force to drop. Where you hit them is also going to affect how much stopping power is needed.

Adding even further to the confusion is the fact some bullets will cause considerable damage to the organs even without a direct hit, due to their stopping power or other traits. And then there’s “Hydrostatic Shock” – a complex topic best left for a different article.

List of Common Calibers

To avoid overwhelming you with too much information, here’s a list of the most common calibers:

• .22LR (LR = long-rifle)
• .25 ACP (ACP = Automatic Colt Pistol)
• .380 ACP (Also referred to as a “9mm Short” in some circles)
• 9mm (officially the “9x19mm Parabellum” or “9mm Luger”)
• .40 S&W (S&W = Smith & Wesson)
• .45 ACP
• .38 Special
• 7.62x39mm (Soviet standard AK-47 round)
• .223/5.56x45mm (actually 2 separate but nearly identical bullets)
• .308/7.62x51mm (actually 2 separate but nearly identical bullets)
• 12 GA (GA = gauge – a shotgun cartridge)
• .50 BMG (BMG = Browning Machine Gun – not common for civilians, but worth mentioning)

Common Bullet Types

Ready for some more terminology?

Full Metal Jacket (FMJ) is easily the most common, consisting of a soft metal core fully encapsulated by a harder metal (for example, lead core and copper jacket).

Hollow Points (HP) expand once they hit their target. They’re the go-to for home defense guns, concealed-carry holders and police officers due to their higher stopping power.

Open-Tip (OTM) look similar to hollow points but don’t effectively expand. They’re the reverse-image of FMJ rounds in a sense. While FMJs are made with small copper cups, with the cup bottom forming the bullet tip, OTM cups form the bottom of the bullet instead. In case you’re wondering, the “M” in the acronym comes from the alternative name for open-tip bullets: Open-Time Match.

Don’t let manufacturers confuse you between an OTM and an HP, by the way (Sierra is one guilty of calling their OTM rounds HP). If it becomes an important difference for you, double-check online before making any purchases.

Ballistic Tips combine the FMJ’s aerodynamics with the HP’s superior stopping power. Essentially, they’re HPs covered with a plastic tip to mimic the more streamlined FMJ.

Soft Points were an earlier attempt at what the Ballistic Tip achieves. Instead of a plastic tip, Soft Points expose some of the inner lead at the tip, which flattens better when striking the target.

Bird Shot is the smallest range of shotgun pellets, packed into the shotgun shell. Great for hunting birds, but not much else.

Buck Shot is the next size up and the best shotgun pellets for home defense.

Slugs are solid 1 oz metal projectiles used in shotguns. They don’t spread, but hurt like hell.


There we go! You’ve just completed your first basic bullet and ammunition crash course! Keep learning more in our Training & Tactics section.

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