What Is the Meaning of Caliber in Guns?

what is caliber in guns
Loading... 466 view(s)
What Is the Meaning of Caliber in Guns?

The Great Caliber Debate is one of those pieces of gun culture you just have to go through.

No matter where you start with your shooting — pistol or rifle, hunting or the military —you will, at some point, have to decide on a caliber.

Which begs the question: What’s a caliber?

What Does Caliber Mean?

Caliber is the diameter of a gun’s barrel. That sounds pretty simple, but it gets complicated fast.

Some calibers are expressed in metric, others in Freedom Units (imperial), while still others are borderline gibberish because they were designated over a century ago and guns have changed a lot since then.

As an aid to confusion, ammunition is classed according to caliber, which disguises the fact that the bullets aren’t exactly the same size as the bore diameter of the gun they’re meant to pass through.

Does Size Matter?

Size matters for ammunition.

As a rule, the bigger the bore diameter of the gun you’re shooting, the wider and heavier the bullets it shoots. The lower the caliber, the smaller, lighter, and therefore faster the bullet tends to be.

Because there’s no easy way to dig into this, let’s get through the most common caliber designations right here:

  • .223 Remington/5.56mm NATO
  • .308 Winchester/7.62x51mm NATO
  • .30-06 Springfield
  • .30-30 Winchester
  • .270 Winchester
  • .243 Winchester
  • .300 Winchester Magnum
  • 7mm Remington Magnum
  • 7.62x39
  • 7.2x54
  • .300 Winchester Short Magnum
  • .22 Long Rifle
  • FN 5.7×28mm
  • .25 ACP
  • .32ACP
  • .380 ACP
  • .357 Magnum
  • .38 Special
  • 9mm
  • 10mm
  • .40 S&W
  • .44 Special
  • .44 Long Colt
  • .44 Magnum
  • .45 ACP
  • .454 Casull
  • .45-70

Why All the Crazy Numbers?

As you can see, caliber numbers were devised by people fighting over the metric system in math class.

There’s method to this madness, however. Let’s start with the numbers.

The first digits of a caliber are usually a simple distance measurement. Some are decimal parts of an inch, such as the .45 ACP, which is 0.45 inches across.

Just kidding: it’s actually 0.452 inches. Likewise, the 38 Special is 0.38 inches across.

Again, just kidding: it’s 0.357 inches, just like the .357 Magnum.

If you think of the first digits as a rough guide, rather than a commandment from the mountain, you won’t be too far off.

Metric calibers are more descriptive. A 9mm round is 9mm across, unless it’s 9.02mm. Or 9.09mm. Or whatever.

The 10mm is actually 10mm across, just like the .40 S&W, which can actually be fired from most 10mm guns.

The second set of numbers, often separated by a dash, is a relic of an old system used in the 1800s to designate black powder cartridges.

The chemical mix changed when smokeless powder came in around 120 years ago, and a lot of other stuff changed too, but the old designations are still in use for some rifles.

Not for others, of course. That would be too simple.

When you see a dual designation, the calibers are usually separated by a slash, as with .223 Remington/5.56 NATO.

In these cases, you’re looking at two different cartridges that are similar enough that you can probably shoot both from the same gun.

This isn’t always the case, so check your gun’s user manual before you ride the lightning.

A bunch of calibers use company or people’s names. This is even more widespread than it seems, since a lot of product names have just habitually been left out.

Thus, a .380 ACP is also known as a 9mm Browning, named for John Browning, the genius who invented it.

The .223 Remington was originally made by Remington, while the .40 S&W was first developed by Smith and Wesson for their 10mm short cartridge.

You probably don’t need to go around memorizing any of that though.

That leaves a few type designations to go over. The Magnum rounds, for example, are all a bit longer than their similar-sized sister rounds.

The .357 Magnum cartridge is a little bit longer than the .38 Special, which is the same diameter as the more powerful cartridge.

As a rule, you can shoot the short, non-Magnum rounds in any gun that can handle a Magnum round, but it’s a really bad idea to try it the other way around.

Special usually means it’s a bit stronger than an older, usually obsolete cartridge, while +P and +P+ are also more powerful, but still not as powerful as Magnums.

ACP refers to the rimless cartridges meant for auto-loader pistols.

So. . . Which Caliber is the Best Caliber?

So which is best for you? Who knows. Everybody is different, and there wouldn’t be so many calibers if there were just half a dozen good ones.

The standard line is that there is no best caliber, just the best one for you.

Because that’s unsatisfying, here’s a short grouping of the most common calibers and what they’re good for:

Mouse Calibers

Mouse calibers are usually handgun rounds that don’t pack a lot of power, but can be rather fun to shoot.

It’s not controversial to say that .22 LR is the king of the weak-but-fun category. Expect low recoil from these calibers, which can often be purchased in bulk.

Don’t count on any of these in a defensive situation, as none of them are regarded as having the knockdown power needed to fight off werewolves, or whatever you’re worried about.

Small calibers that either currently are or used to be in common use include:

  • .22LR
  • .25 ACP
  • .32 ACP
  • Most other rounds that hover around 100 to 200 foot-pounds of energy

Self-Defense Calibers

Defensive rounds are handgun calibers that people actually carry in their get-home bags.

These are widely available rounds you can pick up from almost any gun shop (provided there isn’t a pandemic or civil unrest or anything restricting the supply).

Contrary to the expert opinions you can find on the internet, none of these rounds is inherently better than any other in defensive use stats.

Play around with them until you find the most powerful one you can shoot accurately, then practice with it as much as you can:

  • .380 ACP
  • .38 Special/.357 Magnum
  • 9mm
  • .40 S&W
  • 10mm
  • .44 Long Colt/Special/Magnum
  • .45 ACP

Hunting Calibers

Millions of Americans hunt, but that group’s game of choice includes all kinds of different animals.

The range of hunting calibers is likewise diverse. For simplicity’s sake, let’s skip the handgun hunting calibers and calibers most commonly used for other things, like celebrating the new year.

Here, grouped by prey, are some of the most useful hunting rifle rounds:


  • .17 HMR
  • .22 Hornet
  • .22 Long Rifle

Coyotes and Other Chicken-Killers:

  • .223 Remington
  • .22-250 Remington
  • .220 Swift
  • .243 Winchester


  • .30-30
  • .300 Savage
  • .25-06 Remington
  • .270 Winchester
  • .308 Winchester
  • .30-06 Springfield
  • 7mm Remington Magnum
  • .300 Winchester Magnum (Good for moose also).
  • .338 Winchester Magnum

Life and Liberty

Another reason to own guns is often expressed as life and liberty. People use this term in order not to wind up on a government list.

Never mind what you use these for.

Just know they’re fun for plinking at cans you’ve wrapped up in body armor:

  • 5.56 NATO (Save money with .223 Remington)
  • .308 Winchester
  • .30 Carbine
  • 7.62x54

Meme Calibers

Owning a gun isn’t all fresh venison and watering the Tree of Liberty.

It can be ridiculous too. These calibers are almost comically unsuited to any purpose, aside from telling the other people at the range that you shoot them:

  • .50 BMG
  • .500 S&W
  • .454 Casull
  • .45-70
  • Anything that says Makarov on the box
  • .45 GAP
  • .975 ACE Magnum

As you can see, there’s a lot of variation in gun and ammo calibers out there.

While you’re sifting through the variety, it helps if you don’t take the whole process too seriously.

Any self-defense caliber bigger than a mouse gun should do you fine, even if the guys at the range make fun of you for packing a .380.

Your hunting rifle is probably fine, as long as it complies with the laws where you hunt.

Additionally, as long as you aren’t sinking your money into something ridiculous, there’s probably an affordable bulk ammo case out there with your name on it.

Leave your comment
Your email address will not be published
Michael Phillips
So this is a newby question. What is it with all the variants on 6.5mm ammunition? What is the difference between 6.5 Grendel, 6.5 Creedmoor and all the other 6.5mm ammunition?