Think you are shooting a .38? You probably aren’t.

Most people are aware that modern .38s aren’t .38″ In diameter. They are .357″ or so, closer to a .36 caliber. Fewer people know that a .36 caliber cap-and-ball revolver has a nominal bore diameter of .375″.  So .38s are really .36s, and .36s are really .38s. Confused? You should be- it’s confusing. Most don’t know how this screwed-up state of affairs came about. Here’s how it happened as near as I can reconstruct it-

Let’s start with the muzzle loaders. Typically a muzzle-loader used a slightly smaller ball than the bore, with the difference being made up by the patch.  If you were shooting a .38-caliber muzzle loader these balls were often in the neighborhood of .36 caliber.

Colonel Colt decided to make a medium-caliber revolver, which was introduced in 1851. He called it a .36, because that was the diameter of bullets that a muzzle-loader of .38 caliber used. Except since you didn’t use a patch the bullet needed to be .38 caliber. Why didn’t he just call it the 1851 Navy .38? Who knows? Maybe the thought was that if he called it a .38 people would try to load it with .36-caliber balls. Yeah, it doesn’t make any sense to me either, but it set the stage for 150 years of confusion.

When Colt and others began to make cartridge-conversion revolvers the madness abated briefly. The two flavors introduced for these were .38 Rimfire and .38 Colt. In both cases actual .38-caliber bullets were used, but these were heel-base bullets with the base rebated to fit into a case the same diameter as the bullet (the only common uses of this type of bullet today are .22 Short and .22 LR.) The inside diameter of these cases was about .36-caliber.

These cartridges using heel-base bullets were not an ideal solution as the lubricating band was outside of the cartridge-case and could pick up dust and debris. The solution was to place the bullet entirely inside the cartridge-case. That way the lubrication was protected against dirt or being inadvertently wiped away.  In the case of .38 calibers this meant that you moved to a .36 diameter bullet. Of course you made your revolver with a .36-caliber bore for the smaller bullet.

So why continue to call it a .38? Marketing, I suspect. People were used to buying .38 ammo- easier to just keep calling it that. Besides, maybe .38 sounded more potent than .36 and it made a clear separation between new cartridge guns and the older Cap-and-ball guns. We can only speculate as they didn’t write down their reasoning.

Yep. Your gun is lying to you. 

The .38s aren’t alone of course; the original .44 Colt was .45 caliber to match the .451-.454 diameter bore of cap-and-ball revolvers. No, we don’t know why these were called .44s. Presumably the same sort of reasoning that originally led them to call a .38 a .36. Likewise .44s are .43-caliber. .32s are .31 Caliber. Bullets for.30-calibers are .31. Yeah, it’s kinda’ confusing- and dumb.

The bad part of it is we’re still doing it. .460 S&W Magnum? Yeah, it’s .45 caliber. Federal’s .327 Magnum uses .312″ bullets, being named I presume to distinguish it from .32 H&R Magnum and make an association with .357 Magnum. I guess we can’t look for a sudden burst of rationality from ammunition manufacturers at this late date…

Michael Tinker Pearce, 31 August 17