Caliber designations

C

cdoc42

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I was looking for info about the Remington Ultra Mag and noticed that Wikipedia described it as a 7.62mm (.300 inch)cartridge. This seems to be the common presentation for .30 caliber cartridges in general. But, except for the 32-20 and "7.62x39 M43" all "30 caliber" cartridges fire a .308 inch, 7.82mm bullet. The "7.62x39 M43" actually uses diameters ranging from .308 to .310 (7.87mm) while the 32-20 uses a bullet from .308 to .312 (7.92mm).

This disparity is seen in other calibers as well. The .270 is really .277 (7.04mm) while the "7mm Rem Mag is .284 (7.21mm).

The .264 Rem Mag is listed with the 6.5mm cartridges which all use a bullet diameter of .264 which is 6.71mm.

The .22 caliber cartridges all use a .224 (5.69mm) bullet but are called .222, .223, 22PPC, 219 Donaldson, 219 Zipper, 225 Winchester, 220 Swift, etc.

It is clear that the marketing departments take over when the ballisticians are finished with their discoveries.
 
Is there a question here? Yes the .300 Rem Ultra Mag (I have one) is a .308 caliber, same as .30-06, .300 Win Mag, .308 Win and other standard .30 calibers. The Ultra Mags also come as 7mm, .338 and .375. These are non-belted cases.
 
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Some cartridges are named for bore diameter like the .270 and the .250 Savage. Their respective groove diameters are .277 and .257...The British .303 [bore diameter] is actually .311 groove diameter.

Some cartridges are named for groove diameter like the .257 Roberts. It's bore diameter is .250 and the man that first chambered it was Ned Roberts.

The Europeans name their cartridges in metric terms and are equally misleading as to bore and groove diameters.

Handgun cartridges are really complicated.

The 38cal. revolver is actually a 35 with a groove diameter of .357. The 44 is actually a 42.

Jack O'connor wrote a good chapter on it in the Rifle Book.

Joe
 
Just a clarification: The .44 is actually .429 (almost a .43) . Certainly not a .44 :) ... And in the blackpowder world .44 is really a .45 in most cases... go figure.
 
The marketing departments don't take over. They run the place and have the final say in everything. Including what gets discontinued with no regard for existing customers.
Trying to figure out why a cartridge is called what it is will give you an aneurism.
"...all "30 caliber" cartridges fire a .308 inch..." Nope. However, the .30 calibre designation is about the bore diameter. That's the land to land diameter.
The .270 is not a calibre. It's a cartridge name. So is 7.62 x 39. .303 British is the American name. Brits et al use 7.7 x ×56mmR. And groove diameters can go to .315" and still be considered ok. There's no ammo using that size bullet though. No jacketed bullets either.
32-20 uses a .314" bullet. The 7.62 x 39 a .311" bullet. No .308's for them at all. The .303 Savage isn't. It's a .308. A 7.5 Swiss is too.
The Remington Ultra Mag comes in 7mm, .300, .338 and .375. Only one is a .30 cal.
Wikipedia is an authority on nothing. Anybody with Internet access can post anything they want there.
 
A friend of mine asked a similar question at a group lunch a while ago.

I explained how a .38 special and a .357 magnum both shot the same diameter bullet. I explained how a .44 magnum shot a .429 diameter bullet. I explained how the .45 ACP used a .451 bullet and the old cowboy Colt .45 usually used a .454 to .457 bullet but 'modern' versions of the six shooter used the .451 diameter bullet and how a .460 S&W magnum could fire .454 Casull, .45 Colt as well as .460 S&W magnum ammunition.

After my explanation there was silence at the table and then my friend looked at me for a long moment and said, "Gee Dale if you don't know just say so."

What a wonderful hobby we have here.
 
DaleA, my usual comeback in a situation like that is, "Just because you don't know what I'm doing doesn't mean that I don't know what I'm doing."
 
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