One of the most daunting things when I first started looking for a gun was…what size bullet to get?
We’ll be covering purely bullet size…and the benefits/weaknesses of each. Now, there’s A LOT of sizes 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 a round. By the end, you’ll be a bullet pro!
Table of Contents
Bullet Size & Caliber
For guns, “caliber” 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 Centerfire
- Common Calibers
- Common Bullet Types
- Components of Cartridges
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Rimfire vs Centerfire
The first differentiator is between rimfire and centerfire cartridges.
The rimfire’s primer is built into the rim while the centerfire cartridge has the primer in the center. Rimfires are extremely cheap (few cents each) and the .22LR is the most popular rimfire caliber. For even more differences, see our article on rimfire ammo or familiarize yourself with how guns work.
Common Bullet Calibers
There’s A LOT of bullet calibers, but you might not run into more than a handful in your lifetime. We’ll be going over 18 calibers in total I have on hand, but let’s start with the top 11 most common sizes (in my opinion) first.
Overview of More Common Bullet Calibers
To make things a little more confusing, there’s a mixture of measurements in inches and millimeters. 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 center 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.
Now let’s go through some!
The “twenty-two” long-rifle is the most common caliber 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 caliber 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 centerfire 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 caliber 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.
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-ish 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 millimeter” or “nine mil” for those in the know.
My personal favorite 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 defense.
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.
And now…there’s been a huge rise in popularity of Pistol Caliber Carbines (or PCC). Get the nice ergonomics of a rifle but with the price and hollowpoints of the 9mm.
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.
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.
Designed in 1904 by Mr. John Browning himself for the famous 1911 pistol, this round has one heck of a history.
This thing is a big bullet with stopping power to spare.
The choice of many police officers and military personnel for years, the .45 caliber round has proven itself time and time again. I could probably do an entire article on just this bullet.
It has a large bullet of around 230 grains and has moderate recoil. I can tell you from personal experience that this is not a round to hand to someone who’s never fired a gun before. Its stopping power is renowned and has a nostalgic following.
The “thirty-eight special” is most commonly found in revolvers.
It has manageable recoil but is still quite a handful when in a very light/small revolver. It has a longer cartridge and more powder in said cartridge but it is a slower, heavier bullet than the 9mm. The FBI used this cartridge as its standard issue for a very long time.
The .357 Magnum is identical to the round except for being slightly longer. You can safely fire a .38 Special in a .357 Magnum gun, but don’t try the other way around due to size and pressure constraints. Bullet weights vary from 110 to 132 to 158 gr.
The Soviet round used in the AK-47 line of rifles. It has moderate recoil, great knockdown power, and a bullet weight of usually 123 grains.
There is a high availability of military surplus ammo which makes the round very affordable.
.223 / 5.56x45mm
The “two-two-three” (inch) Remington has almost the exact dimensions as the “five-five-six” (mm) NATO cartridge.
The 5.56 has higher pressures than the .223, so .223 rounds can be fired in a 5.56 rifle, while 5.56 rounds should not be fired in a .223 rifle. Bullets are around 55 grains and the cartridge has light recoil.
It is the ammunition used in the M16/M4/AR-15 line of rifles and there’s still endless debate on its effectiveness in combat.
However for civilian shooters who get the benefit of hollow point ammunition…it is strongly recommended for home defense.
.308 / 7.62x51mm
The “three-oh-eight” (inch) Winchester is almost the same dimensions as the “seven-six-two” (mm) NATO round.
There are special considerations when mixing the rounds but unless you know what you are doing, stick with the round intended for your rifle.
It is a popular hunting round with moderate recoil, high stopping power, and a wide range of bullets available from 150 to 208 grains.
The most popular shotgun round.
20 gauge is a smaller round while 10 gauge is a much larger round.
Recoil can vary from moderate to high based on round.
Shotgun ammunition is the most versatile with birdshot (lots of smaller metal balls), buckshot (fewer much larger metal balls), and slugs (1 oz piece of solid metal).
Here is a pump-action shotgun with birdshot…
Stopping power is renowned with buckshot and slugs (even more recoil) but there’s a price to be paid!
Not really common for civilians, but I just had to have it in here. It’s huge and has huge recoil with awesome range (confirmed kills at 2000m+), and you definitely don’t want to be on the receiving end of the bullet. 660 grains of pure stopping power.
Common Bullet Types & Terminology
Still with me?
I’ll go over rarer types of calibers at the end of the article since I really want you to learn about the common bullet types first.
Full Metal Jacket (FMJ)
This is the most common type of bullet and consists of a soft metal core, such as lead fully encapsulated by a harder metal, such as copper. They are usually pointy, round, or even flat. Wound channels are typically small and go through a target.
Great for the range but not preferred for defensive rounds.
Hollow Point (HP)
Hollow points are made to expand once they hit something. They are the go-to round for police officers, concealed weapon carriers, and home defense guns because of their stopping power.
Below you can see the difference between a round nose 9mm FMJ and a hollowpoint:
Open Tip (OTM)
Open-tip bullets look like hollow points since they have an opening at the top, but this is more because of their manufacturing process. The openings are too small to expand effectively.
Regular FMJ’s are created from small copper cups where the bottom of the cup becomes the tip of the bullet. Open-tip bullets are the opposite, with the bottom of the cup becoming the bottom of the bullet.
Open-tip bullets are sometimes also known as Open Tip Match (OTM) since they are preferred by long-distance shooters. The manufacturing process for open tip bullets creates a more consistent round than FMJ. Important when you’re shooting hundreds of yards!
To make things more confusing, several manufacturers such as Sierra still call their open tip rounds “hollow point.” If it is important to you, it is best to check online or call.
This is what you get when you combine the aerodynamics of an FMJ with the stopping power of a hollow point. This is a hollow point covered with plastic to mimic the profile of an FMJ. They are usually used in hunting.
Below you’ll see that the bottoms of the bullets are more streamlined. This design is called “boat tail” and produces less drag as the bullet flies through the air. HPBT is short for “hollow point boat tail.”
This is an earlier attempt to get the ballistic advantages of an FMJ with better expansion.
In soft point bullets, part of the lead is exposed at the tip. The softer lead is designed to flatten better when the bullet hits a target. But for the most part, ballistic tips have surpassed the performance of soft points.
Note that the left and right bullets are boat tail while the middle one is not.
We’re back to shotgun rounds.
Birdshot consists of the top row and is pretty small pellets numbering in the dozens in each shell. Here’s a 7.5 shot shell with a clear hull.
Great for hunting birds and blasting clay pigeons, but not the best for home defense.
The overall best home defense round is buckshot. 00 (“double-aught”) is the go-to load.
Slugs are single projectiles that are around 1 oz of solid metal that really bring the hurt. However, they don’t have the spread of birdshot or buckshot. But, in the hands of a solid shooter, they can be accurate up to 100 yards.
Components of Common Cartridges
What makes up a cartridge?
If you get into shooting, you’ll see the costs can really add up. That is when you get into reloading your own ammo. Here are just a couple breakdowns of the calibers I currently reload. You can see the difference in powders & bullets for each type.
Less Common Bullet Calibers
Let’s quickly go over the remaining 8 calibers I have on hand:
If you remember, the .40 S&W is just a cut down version of the 10mm which is pretty tough to handle and not something I want to be shooting all day at the range.
Which is just the reason the FBI downgraded from the 10mm to the .40 S&W (and now to the 9mm). Great stopping power and harsh recoil.
Made by FN for their P90 personal defense weapon (PDW) and Five-Seven (get it?) pistol. The small bullet (23-31 gr) travels very fast and allows for increased penetration with low recoil and high magazine capacity.
The history of this little guy is interesting if you’re into that kind of thing. This is a round born of the Cold War when Western European nations were worried about the Soviets invading, specifically worried about paratroopers wearing body armor.
The design of the P90 and the 5.7 go hand-in-hand, the goal of each being to equip rear echelon troops with a weapon that was easy to handle, easy to transport, and still effective Vs. regular troops wearing body armor.
Although the Soviets never invaded, the P90 and the 5.7 have proven themselves to be very effective in that role. However, if you’re not facing attackers wearing body armor – there are better options.
Hands-on review of the FN Five-seveN!
A beefed up .38 Special almost exclusively for revolvers. Great reputation for stopping power but at the cost of some decent recoil. Bullets vary from 125 to 158 to 180 gr.
Need ammo? Best .357 Magnum Ammo!
Light rifle round designed for the M1 Carbine that was introduced in the 1940s. Used in service even up to the Korean war, the round and rifle still have a popular following in the civilian world. The standard bullet is 110 gr.
Designed to give the ballistic performance of the larger .30 caliber AK 7.62x39mm round but designed for the AR-15 and using standard magazines at normal capacity. Thus, the case is a shortened 5.56 case to fit reliably. Getting more popular as it is a great round for suppressed shooting out of short barrels. Bullet weight ranges from 110-220 grain.
Designed by the Russians for their Mosin-Nagant, and then used in more than a dozen guns ranging from rifles to LMGs, and still in use today in the Dragunov and other sniper rifles, which makes it the oldest cartridge still in combat use. Slightly more recoil than a .308 Winchester. Bullet weight is around 140-200 gr.
The “thirty-aught-six” is one of the US’s oldest cartridges, introduced in 1906 and the primary military ammo for almost 50 years. Strong recoil, and with it range, but tolerable by most shooters which makes it still beloved by many shooters around the world. Bullet weight is around 150-180 gr.
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