Why so many diameters?

And don't forget a .44mag is really .42"

I've tried .357" diameter in my 9mm revo and they grouped quite well.

You didn’t even mention .44 Mag handgun is .429 and rifle is .431. I once heard that in Europe .309 was more popular than .312 in .32 ACP so I checked my stash and sure enough the Geco, PPV, & S&B were .309 and the American stuff was .312. If you measure 22 LR ammo you’ll find diameters from .221 to .223 and some times other variations. Many 9mm bore diameters are greater than .355 and .357 bullets can actually be more accurate in some guns.

What does that all mean? A wide variety of diameters will work in guns and that you should always test your ammo to figure out what works best in your gun.

Many of the standards mentioned in the OP were decided a long time ago and the various gun designers kind of did their own thing. It’s kind of amazing that so many of the popular calibers ended up being so close to one another.

Figured out by COMPETITORS.
If my bullet is to be better than yours, it must be DIFFERENT.
Add in Inch vs metric conversion and approximation.
Consider manufacturing tolerances, they are wider than you might expect.

Were some cartridges created so the bullets could not be used in a adversaries gun?

7.62x39 in foreign rifles like AK’s = .312
7.62x39 in Ruger= .308.
They can be used interchangeably though.

There are many examples of this.

Robert said:

45 rifle is .458 and 45 pistol, like ACP, is .451..

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While the 45 colt, 454 casull, and 460, are .452

Well, at least my 40S&W is .400!.... unless, of course I shoot cast in .401.

If all the calibers were standardized it would be such a boring world.

Disparity in named size vs. actual size is not new. From the 1870's .44-40's were actually 42 caliber and .38-40's were actually 40 caliber.

You wonder why someone at Winchester decided this was OK.....

.38-40 and .40 S&W can use the same size and weight bullets and actually have similar performance.

Robert said:

45 rifle is .458 and 45 pistol, like ACP, is .451..

Click to expand...

Or 452 or 454.

There has never been any standard for firearms although there have been attempts to standardize some things. Each inventor could do whatever they wished and name it whatever they want. Then you have the English measurement system and metric and depending on where something was invented things change. In Germany it is 7X57, in England 275 Rigby, and in the USA the same cartridge is referred to as 7mm Mauser.

Variety is the spice of life. Think how much is sold to people thinking "this caliber might be just a little better than the caliber I'm shooting now" and so on and on. Increased sales, increased profits, and it gives us shooting junkies something to do.

Speedo66 said:

Disparity in named size vs. actual size is not new. From the 1870's .44-40's were actually 42 caliber and .38-40's were actually 40 caliber.

You wonder why someone at Winchester decided this was OK.....

.38-40 and .40 S&W can use the same size and weight bullets and actually have similar performance.

Click to expand...

The 38-40 situation came about as a clerical error. The cartridge designation should have been 40-38 - 40 caliber with 38 grains of black powder - but somewhere the numbers got reversed and no one caught it until after it was released.

Bob
NRA Benefactor Member

Bob Willman said:

The 38-40 situation came about as a clerical error. The cartridge designation should have been 40-38 - 40 caliber with 38 grains of black powder - but somewhere the numbers got reversed and no one caught it until after it was released.

Bob
NRA Benefactor Member

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That's a good theory, but since the original name of the cartridge was the 38 Winchester, how could the numbers have gotten reversed? There was only one number. 38.

Like alot of things the answer is history.

The naming of bullets and calibers did not begin with some international body of cartridge namers based in neutral Switzerland. It began in different countries and often by competing companies or arsenals. So each country and each company followed their own traditions and in the case of companies what they thought would sell.

After the Great French Revolution of 1798 introduced the metric system to Europe it looked like it might sort itself out, but no.

Some nations continued to build bullets by caliber rather than metric designations. Two different systems of measurement.

There are a good many names that are names for rounds because they sound "right" to the marketeers. Or because they remind folks of another round that is popular. This continues till today. Would the 300 AAC Blackout sound as good as the .308 Blackout? Or the 7.62 x 35 Blackout? The developers at AAC of the round didn't think so.They called it the 300 Blackout.

Here's something else to look up...why so very few cartridges, for any type gun, in 10mm or 40 caliber named beginning with the 40 or the 10. We have 38-40, 44-40, 44 Spl. etc. We have the 10mm and the 10.57 Lazzeroni Meteor. But naming a round beginning with a 40 has never been popular.

In terms of actual calibers the trend has been towards fewer various dimensions for a century now.

Great, now my head hurts...

Speedo66 said:

Disparity in named size vs. actual size is not new. From the 1870's .44-40's were actually 42 caliber and .38-40's were actually 40 caliber.

You wonder why someone at Winchester decided this was OK.....

.38-40 and .40 S&W can use the same size and weight bullets and actually have similar performance.

Click to expand...

For a short time Roger made a Blackhawk with 40S&W and 38-40 cylinders.

BigBore44 said:

7.62x39 in Ruger= .308.

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FYI, According to Ruger customer service this was corrected about 20 years ago. They can give you the serial number where it changed in the 180 series. All the 580 series have the bigger bores.

Add to all this the way different countries measured bore diameter in the 1st half of the 20th Century. Some are measured as land diameters, while others are groove diameters.

Then there is the “American” 8mm Mauser. AKA, 7.92x57mm J shooting .318” diameter bullets, or the 7.92x57mm JS using .323” bullets.

And, 6.5s are pretty standardized at .264”. Except for the 6.5 Carcano at .268”.

Wyman

tipoc said:

Here's something else to look up...why so very few cartridges, for any type gun, in 10mm or 40 caliber named beginning with the 40 or the 10. We have 38-40, 44-40, 44 Spl. etc. We have the 10mm and the 10.57 Lazzeroni Meteor. But naming a round beginning with a 40 has never been popular.

Click to expand...

I better tell the .40-65 in the next room that it is one of a very few. Along with the .40-82 down the street.
Does the .450/.400 count? The British put the parent cartridge first, the neckdown second, unlike Us Colonials.
Do the .402 Enfield and .405 WCF qualify or does that third digit interfere?

Jim Watson said:

I better tell the .40-65 in the next room that it is one of a very few. Along with the .40-82 down the street.
Does the .450/.400 count? The British put the parent cartridge first, the neckdown second, unlike Us Colonials.
Do the .402 Enfield and .405 WCF qualify or does that third digit interfere?

Click to expand...

Yeah, the last three you mentioned don't count, obviously. Obsolete British sporting cartridges do include some 40s as does the old Sharps. But they go more to prove my point. Not alot of "40 calibers" out there named such, particularly in this century.

jdh said:

FYI, According to Ruger customer service this was corrected about 20 years ago. They can give you the serial number where it changed in the 180 series. All the 580 series have the bigger bores.

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IIRC, this was done per special order for South Africa....

Don't forget the 7.63 Borchart, Luger, and Mauser cartridges that Russians re-barreled down to 7.62, only because they were dirt poor and didn't have much in the way of gauges, so it was much easier for them to make same-size barrels for everything.