There are many myths, misconceptions, and legends about various guns and ammunition, including the differences between gun calibers and bullet calibers, and it seems like everyone who knows anything about firearms considers themselves an expert. The language of firearms has evolved with few rules, and as a result there is a lot of confusion. This won’t solve everything, but here are some things I’ve learned, when I was looking up other things.

Tip 1: Caliber vs. Gauge.

Gauge is a measure of the inside diameter of a shotgun barrel, while caliber generally refers to the diameter of rifle and handgun bullets. However, a .410 is the caliber of a small shotgun, which is never called a 67½-gauge. Gauge was developed hundreds of years ago, before accurate devices allowed for precise measurement.

Tip 2: Caliber.

Caliber refers to the diameter of a bullet, and can be expressed in either metric (7mm) or English (.284) measurements, depending on where it was developed (Europe or the U.S.), or the whims of the marketing department of the company that first designed the bullet.

Tip 3: Numbers Aren’t Always Exact.

The .38 Special and .357 Magnum are both 38-caliber, but the bullet is actually 357-thousandths of an inch in diameter. The .30-30, .30-06, .300 Winchester Magnum, and .308 are all different, non-interchangeable rounds that are all 30-caliber. However, 30-caliber bullets are .308-inches in diameter. I once saw a customer go ballistic (pun intended) because he wanted to handload his .30-30, and the clerk gave him bullets that were .308-inch in size. The clerk was right.

Tip 4: Those Other Numbers.

So if a .30-30 and a .30-06 are both 30-caliber rounds, that are .308-inch in diameter, why do they have those extra numbers? In the case of the .30-30, it meant that there was originally 30-grains of smokeless powder inside the case. However, for the .30-06, the -06 has nothing to do with powder—that was the year, 1906, that the round was adopted by the U.S. Army. There are other cartridges, such as the .30-378 Weatherby Magnum that is 30-caliber (.308), but it used a necked-down .378 case. And then there are rounds like the 7.62×39 and the 7.62×51, where the 39 and 51 refer to the length of the case.

Tip 5: Never Assume.

A .22 LR (long rifle) is much different from a .220 Swift, a .22-250, or a .22 Hornet. A .300 Winchester Magnum will not work in a .300 Weatherby Magnum, and you can’t buy a spacer to make a .300 Super Short Magnum work in a .300 Short Magnum. I was once ridiculed by a friend when I wanted to buy a .44 Magnum rifle, because everyone knew that the .44 Magnum was a handgun cartridge. The joke was on him, as there are a number of rifles chambered to shoot handgun rounds, and a few handguns that shoot some rifle cartridges.

Tip 6: Other Language Problems.

Language is constantly changing, and the rules can change as popular usage changes. It drives me nuts when a gun’s magazine is called a “clip.” However, I often use the word “bullet” to indicate an individual round or cartridge, even though the bullet is actually just one component of that cartridge.

Tip 7: Why So Many?

Looking through a reloading manual, I found bullets with actual diameters of .257, .264 (6.5mm), .277, and .284 (7mm). Do we really need bullets in so many diameters that are so similar? Well, I don’t need them, but someone does. Bullet diameter is only one variable in the performance of a particular round. The case size and shape, as well as the kind of powder and primer, all have an effect on the downrange performance. To each his own.

Photo: Jean Skillman, U.S. Army Environmental Command

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5 thoughts on “Understanding Gun Jargon: Calibers and Gauges

  1. I have a 32 Winchester Special Model ’94.  Why 32 and why is it special.  When I mention the rifle, some people think I’m talking about a pistol.

    1. Just like this article says, there’s hardly anything “standard” about naming conventions for calibers and gauges, so why precisely it’s got a qualifier of “special” is up to whoever named it. The “.32” comes from the bullet’s diameter, which is .321 inches. People often confuse it with a pistol because .38 Special is a common round for revolvers.

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