We’ll be covering purely bullet size…and the benefits/weaknesses of each. Now, there’s A LOT of sites out there but I want to cover the ones you’re most likely to see and/or use. These are the ones that you can walk into just about any sporting goods store and buy.
Then we’ll follow up with some bullet terminology and the different types of bullet tips (hollow point, etc), how shotgun shell sizes work, and a breakdown of the components of around. By the end, you’ll be a bullet pro!
Bullet Size & Calibre
For guns, “calibre” means the diameter of the barrel and thus the diameter of the bullet that is going through it. Also for terminology sake, “bullet” just means the metal projectile, while the entire thing is called a cartridge.
We’re going to cover a lot in this article, including:
Rimfire vs Centrefire
Common Bullet Types
Components of Cartridges
Rimfire vs Centrefire
The first differentiator is between rimfire and centrefire cartridges.
The rimfire’s primer is built into the rim while the centerfire cartridge has the primer in the centre. Rimfires are extremely cheap (a few cents each) and the .22LR is the most popular rimfire calibre.
There’s A LOT of bullet calibres, but you might not run into more than a handful in your lifetime. We’ll be going over 18 calibres in total I have on hand, but let’s start with the top 11 most common sizes (in my opinion) first.
To make things a little more confusing, there’s a mixture of measurements in inches and millimetres. There’s also a unit of weight called a “grain” which is used to denote the weight of bullets. A “grain” is really small since 7000 grains make up one pound. When you talk about bullets at this high of a level, the most high-level trait is “Stopping Power”. This is a relatively vague trait and somewhat controversial. What it boils down to is how many bullets does it take to drop a person. Granted, if you hit someone in the right spot it only ever takes one but in most situations, you’re aiming for centre mass (a.k.a. the chest, a.k.a. the largest target available). Some bullets have enough power or other traits that will cause damage to organs even if you don’t hit them directly. You might also hear about a term called “Hydrostatic Shock” but that’s an entire article unto itself.
The “twenty-two” long-rifle is the most common calibre in terms of units sold. It has a bullet weight of around 30-40 grains and is extremely mild shooting in both pistols and rifles. The recoil is almost non-existent which makes it a great starter round for someone who has never shot a gun or is uncomfortable with the noise. The low price of the bullets is also great for learning sight pictures. It is traditionally the starting calibre for shooters. These things are only a few steps up from a pellet gun round. They can kill, don’t get me wrong, but they’re mostly for killing rats, snakes, and birds. They’ll kill an attacker for sure but it might take a shot or six. I have extremely fond memories of earning my Rifle Shooting merit badge with a .22LR. Many popular handguns and rifles have .22 versions or adapters that let you practice on the platform but use the inexpensive .22LR ammo.
Slightly larger than the .22 and slightly more powerful….though not much. The ACP stands for “Automatic Colt Pistol.” There are quite a few guns that use this size but the ammo is more expensive and you’re not getting too much added benefit other than the inherent reliability that comes with centrefire casings. Slightly more stopping power than the .22 but it’s kind of like the difference between stabbing someone with an ice pick or a knitting needle. Both do the job, but one will leave an ever so slightly larger hole. It’s a tiny round and I’ve yet to use a .25 calibre gun that didn’t work like crap. I’ve used a few flawless .22’s, however. I don’t know why that is.
Now we’re getting into the beefy sizes. Personally, I would never use a gun with anything smaller than a .380 as my primary carry weapon. Sometimes called a “9mm Short”, it has seen a major boost in popularity recently thanks to the various “pocket pistols” that have come on the market. This is also a very controversial round. If you ever want to troll a gun forum, just go there and ask “Which is better: a .380 or a 9mm?” or “Does a .380 have enough stopping power to use it as a carry?” Watch the arguments start. It’s entertaining. This bullet has relatively low recoil and, at close range, good penetration. They’re a great carry weapon size, in my noobish opinion. Gun author Massad Ayoob once said of the.380 “Some experts will say it’s barely adequate, and others will say it’s barely inadequate”. This is a low power round. Because of the nature of the bullet and the guns that shoot it, it’s going to be relatively useless beyond close-is range.
This pistol round is officially known as the “9x19mm Parabellum” or “9mm Luger” to distinguish it from other 9mm rounds, but you will be fine just saying “nine millimetres” or “nine mils” for those in the know. My personal favourite and if there was a “Goldilocks” round, this would be it. The very first gun I bought was a 9mm. They’re fun at the range. They’re good for defence.
Believe it or not…or actually believe it because it’s true…the 9mm bullet is the same diameter as the bullet used in the .380 and the .38 Special. The difference between the three is the amount of gunpowder behind it and possibly bullet weight. It is the standard round for NATO countries and the majority of police forces around the world. It is mild shooting, can vary in weight from 115-147 grains, and has varying stopping power based on the type of bullet (hint, go with hollow points).
The rounds are inexpensive and they have very low recoil. Many, many guns use this size as well. A compact 9mm gun can be used for concealed carry. Most of the guns that use this size can hold on average 15-17 rounds in the magazine.
Remember how I said the 9mm was the “Goldilocks Round”? If that’s the case then the .40 is her big, angry, whiskey-drinking sister. Originally designed for the FBI as a reduced 10mm cartridge and popular with other law enforcement agencies ever since. More kick when compared to the other popular handgun cartridge, the 9mm. Weights of the bullet can vary from 155 to 165 and 180 gr. Ammo is still relatively inexpensive.
Note that the FBI recently decided to move back to the 9mm since agents are able to shoot more quickly and more accurately with 9mm compared to the .40 S&W