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Old June 16, 2000, 11:05 AM   #1
Futo Inu
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OK, I'm showing that 7.62mm exactly equals .3000". However, my understanding is that .30 rifle cartridges have a bullet diameter of .308, which is 7.82mm, NOT 7.62. So why then are the 7.62 NATO round, and other .30 rounds labeled 7.62, called what they are, rather than "7.82 x ____"? Are they not .308? Seems very silly to get so specific as to go to the hundreths of mm, yet be off by 2/10ths, or 20/100ths, of a mm in the designation. Is my math just incorrect?
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Old June 16, 2000, 11:23 AM   #2
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Why is .38 caliber, .357" or .44 caliber, .429"...makes no sense really...that's just the way it is. I believe that the 7.62 relates to the bore diameter measured over the rifling.
Old June 16, 2000, 11:49 AM   #3
Mal H
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I believe WW is correct. Most European rifle calibers are expressed in diameter of the bore and most American calibers are expressed in diameter of the bullet. But, he hastens to add, there is no hard and fast rule on this on either side of the pond.
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Old June 16, 2000, 01:39 PM   #4
Futo Inu
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Well, no, .357 is sometimes called ".38 special" as a marketing tool (bigger is better, ya know). Likewise, .429/.30 is called .44 special or mag as a marketing tool, but they're not called something really specific in error, such as ".387 special" or ".443 Magnum" for example. I understand that virtually no caliber names exactly reflect the correct diameter, but there is always a reason or story behind the difference. But here I cannot see one, unless what you're saying is perhaps the land (or is it groove - which one is smaller?) is 7.62mm/.300" in the "7.62" cartridges, whereas the larger (groove?) diam is 7.82mm/.308".

[This message has been edited by Futo Inu (edited June 16, 2000).]
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Old June 16, 2000, 02:24 PM   #5
Mike Irwin
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At one time, a long long time ago (generally prior to 1895), a .38 caliber round actually WAS .38 caliber... The same is true with many other old calibers whose bullet diameter no longer seems to match the name of the cartridge.

The .38 Smith & Wesson and the .38 Colt rounds, including the Short and Long Colt, and later early variants of the .38 Special, which was developed from the .38 Long Colt, actually did use .380+ caliber bullets.

At one time, all of these rounds (an many others) were loaded with what is known as a "heeled" bullet. A heeled bullet looks a little like a mushroom, with a larger diameter front part, and a smaller-diameter shank, or in this case, the heel.

The heel fit into the case mouth, and when the bullet was fully seated, the exterior of the case mouth and the largest section of the bullet are the same diameter.

In the case of the early .38s, the bullet and case mouth were nominally around .3800 to .3860, depending on the manufacturer; in other words, the .38 Long Colt and .38 Special actually WERE true .38s!

About 1890-1900 (I pick 1895 as a convenient split) ammo companies came to the realization that ammo using heeled bullets was a pain in the butt to manufacture, so they started changing from a heeled bullet to a bullet that was the same diameter as the heel section.

Voila! Bullets for the .38 Spl. went from .380 more or less to .357! Same was true with other rounds.

That, however, didn't take into account a lot of older guns that now had oversized bores. To accommodate those guns, the ammo companies started loading bullets that large cavaties in the base with thin skirts that would, up on firing, expand into the rifling.

The heeled bullet is still with us today, though. The most common example of a heeled bullet today is the .22 Long Rifle.

When you look at a .22 cartridge, you'll see that the case mouth and the bullet are the same diameter. What you won't see is the smaller diameter heel that is inserted into the case mouth, which holds the bullet and case together.

Beware the man with the S&W .357 Mag.
Chances are he knows how to use it.
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Old June 16, 2000, 03:45 PM   #6
Paul B.
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Futo. 7.62/.300 is the bore diameter. >308 is the groove diameter. Military uses the bore diameter which coincides with European system (NATO) and commercial uses groove diameter, IE, .308. Clear as mud huh?
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Old June 16, 2000, 04:04 PM   #7
Chad Young
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Now, for more confusion, you can read that 7.62mm is also different for different countries! Russian 7.62x39mm ammo is .310 inch in the 7.62x39 round. NATO 7.62x51mm is .308 inch. Also, 8mm Mauser can be either .318 for JR bore or .323 for JS bores.....

If you ever get confused, check the nominal bullet diameter in a reloading book.
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Old June 16, 2000, 06:37 PM   #8
Art Eatman
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Futo Uno: First came the .38 Special--which, as Mike said, is really .357. The .357 Magnum was made with a case which is 1/8" longer so it couldn't be loaded into a .38 Special revolver, thereby creating shrapnel.

Same for the .44 Special and the .44 Maggie.

More little oddities: For some reason, some 50 years back, bullets for .22 centerfires came in .223, .224, .226 and .228. I think it was the Swift which took a .224 bullet; life could get very exciting if you loaded hot with a .228!

I think the .219 Zipper was measured across the lands, not the grooves.

I haven't miked any 30-caliber bullets, lately, but they used to be 0.3085 in diameter. Of course, it's easier to say, "308".

Really, there are some questions which are better left unasked; the answers will confuse anybody. Me, too, and I wuz there! "There's no reason for it; we just did it that way."

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