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Thread: Why are some cartridges a very different diameter then there Name.

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    Default Why are some cartridges a very different diameter then there Name.

    This is a question that has bothered me for some time. Most Cartridges have names that at least are close to there barrel bore or grove diameter. Say the 45-70 which uses a barrel of .450 bore diameter and .458 grove diameter. Or the 7mm Mauser which uses a .284" (7mm) grove diameter.

    I am not talking about small changes of a thousandth or two, too differentiate it from an other cartridge. Or minor changes in diameter due to manufacturing tolerances or slightly larger lead bullets.

    What puzzles me are some of the cartridges for which are way off in name. Take for example the fallowing. 32 S&W = .312" grove diameter, 38 special = .357" grove diameter, and the 44 mag or special = .423" grove diameter.

    I can only assume that this is due to something in the switch from mussel loading to cartridges but have no idea why.

    Does anyone know the story here?

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    Default The simple answer:

    Quote Originally Posted by bandhmo View Post
    This is a question that has bothered me for some time. Most Cartridges have names that at least are close to there barrel bore or grove diameter. Say the 45-70 which uses a barrel of .450 bore diameter and .458 grove diameter. Or the 7mm Mauser which uses a .284" (7mm) grove diameter.

    I am not talking about small changes of a thousandth or two, too differentiate it from an other cartridge. Or minor changes in diameter due to manufacturing tolerances or slightly larger lead bullets.

    What puzzles me are some of the cartridges for which are way off in name. Take for example the fallowing. 32 S&W = .312" grove diameter, 38 special = .357" grove diameter, and the 44 mag or special = .423" grove diameter.

    I can only assume that this is due to something in the switch from mussel loading to cartridges but have no idea why.

    Does anyone know the story here?
    The simple answer goes like this:

    The diameter of the .38 cartridge case is nominally .379". Chamber dimension, then is right around .38". The thickness of the brass, then makes it impossible to have a .38" diameter bullet because it has to fit INSIDE the brass cartridge, whose walls are about 0.010" or 0.011" thick.

    The bullet, then, must be .379" minus .011 twice, or .357" or it will bulge the case and not fit in the .38" chamber.

    If you invent a cartridge, you can name it what you want.

    Your supposition about the genesis of the oddities is correct, but I suspect that there were mis-matched names and dimensions even before that.

    When the chambers of percussion revolvers' cylinders were through-bored to accomodate cartridges, the chamber was the same diameter all the way through, so the bullet diameter was the same diameter as the OUTSIDE of the cartridge. Modern bullets are sized to fit INSIDE the cartridge.

    To fit the full-size diameter bullets into the case, the bullets had a rebated base (the back half of the bullet would be .357" diameter, which would fit inside the cartridge case and the front half was 0.38" in diameter to engage the rifling.

    For practical reasons (so lubrication could be kept inside the cartridge case where it would not get rubbed off and other reasons) the rebated base went away, but the sizing and naming conventions now give us these odd names and sizes.

    A proper historian would be able to do a better job of the explanation and I declare that I am not one. But what I have learned and reported here is reasonable and has a ring of truth to my ears. I imagine this explanation covers most of the mis-matches between names and dimensions, but not all. Anybody else have stories to tell? (Not including the 45-70 which was a .45 caliber bullet over 70 grains of black powder)

    Lost Sheep,

    Remember, only believe half of what you see and one quarter of what you hear. That goes double for what you get from the internet. Even this post. Maybe especially this post.

    Also remember, even the idiotic stuff might have a kernel of truth buried in there somewhere.
    Last edited by Lost Sheep; 02-26-2009 at 00:18. Reason: add the 45-70 comment

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    It's because the Government doesn't regulate Cartridge Names.

    As far as I know, there haven't even been any studies to determine the cost, this inconvenience to the consumer, has created, in real dollars.

    There are, in addition, Safety Considerations, when poorly named cartridges are fired in the wrong guns, because of the confusion.

    We need to send letters, emails, and even petitions, to President Obama, and Senator Mark Begich, and get this issue to the forefront, and dealt with, before any more children have to suffer.

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    Good point Smitty, you start and I'll sign.

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    Quote Originally Posted by bandhmo View Post
    Or the 7mm Mauser which uses a .284" (7mm) grove diameter.
    You want a little more confusion!

    I'll just make a statement about one of your initial assertions. That is that a 7mm Mauser uses a 7mm bore diameter, it does not. 7mm is smaller than a 270 Win (.277). A 270 is a lot closer to 7mm than any 7mm caliber rifle and 7mm is closer to .270 than a 270 Win.

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    Actually, a big part of it is marketing. Which sounds nicer .277 Winchester or .270 Winchester?
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    There is a lot of confusion and there are two basic reason for the confusion. In this country we name a caliber (more or less) based on the bullet size which is the groove diameter of the barrel, not the bore diameter, which is the way they name them in Europe. And in the case of the 7mm it is close to a 7mm bore but not groove. The bore diameter of a 7mm is .276" Or to be exact the metric conversion of a 7mm would be .27559", 276" seems close enough. The groove diameter for any modern rifle is usually .008" larger, giving .004" depth of rifling. So the 7mm bore size takes .284" bullets for its .284 groove diameter. The American 284 Winchester uses .284" bullets.

    The 8mm Mauser, originally called the 7.9mm was .311" bore, which oddly enough corresponded to the groove diameter of the English 303 British cartridge which has a groove diameter of .311" (.303" bore plus .008" of rifling) makes for a groove and bullet diameter of .311". But the 7,9 (8x57) Mauser used bullets of .318" diameter to fit its groove diameter. It was later changed to the 8X57 with the .323" size of the spitzer bullet. (Which is the 8mm divided by 25.4 (mm's to the inch) to equal .315" bore +.008" gives .323" groove and bullets.) Both the English and Germans used bore diameter to name these rifles.

    Naming of a cartridge is also a marketing strategy in this country. Lets consider the various 338 caliber cartridges. 338 Win mag, 330 Dakota,the 340 Weatherby and the 33 Winchester all shoot the same bullet diameter. They are all 33 caliber guns that shoot .338" diameter bullets. Here again bore diameter .330", groove diameter .338". A 30 caliber rifle will have a .300" bore and shoot .308" bullets, even with the mix of names. 300 Wby/Win mag, 308 Winchester, 30 Gov't '06, 300 Savage, 300 Dakota and the 30 Herrett. The 375 H&H is a .375" groove as is the 376 Steyr and the 378 Weatherby, just a twist on the name.

    Some of the names aren't even close to bore or groove diameter, some are exact. The 404 Jeffery was neither .400" or .404" in bore or groove. It was .416" bore (to match the groove diameter of the 416 Rigby) and .423" groove and bullet diameter. The 500 Jeffery was .500" bore and uses .510" bullets (.005" of rifling depth). The 333 Jeffery used .333" bullets but the 475 Jeffery #2 used .488" bullets. William Jackman Jeffery was never good with numbers I guess.

    The 505 Gibbs uses .505" bullets and has a groove diameter of .505"

    Some of the older black powder cartridges were named from the bore diameter and used various bullet sizes because of the less than precise rifling cutting equipment, or because of one to many passes with the cutter hook. Also those guns generally used soft lead bullets and tighter fitting oversized bullets were more accurate.


    As Smitty said; mostly the handgun calibers are named to correspond to the case diameter because of the conversion from muzzle loaders. They kept the cap and ball name but changed the bullet diameter to fit into the case. 32, 38, and 44 were all previous cap and ball revolvers and pistols. I don't think the 41 and 45 were ever cap and ball guns so they are very close to the actual diameter, 41 is .410" the 45 caliber .452" bullet. (was originally .454")

    I don't see why this is confusing?!
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    Quote Originally Posted by Murphy View Post
    As Smitty said; mostly the handgun calibers are named to correspond to the case diameter because of the conversion from muzzle loaders. They kept the cap and ball name but changed the bullet diameter to fit into the case. 32, 38, and 44 were all previous cap and ball revolvers and pistols. I don't think the 41 and 45 were ever cap and ball guns so they are very close to the actual diameter, 41 is .410" the 45 caliber .452" bullet. (was originally .454")

    I don't see why this is confusing?!
    Murphy:
    It was 'Lost Sheep' who said that, so I'm glad you confirmed it.

    Your right. It's not confusing. You just gotta know.

    Smitty of the North
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    Quote Originally Posted by Smitty of the North View Post
    Murphy:
    It was 'Lost Sheep' who said that, so I'm glad you confirmed it.

    Your right. It's not confusing. You just gotta know.

    Smitty of the North

    Oops! Sorry Larry, I'll give you credit for what Smitty does sometime.
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    Murphy, I have been wondering this for some time and this was a perfect explanation. Guess I was kinda right when I kept refering to my brothers .308 as his ".300 short". Thanks again, A+

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    Quote Originally Posted by hunt_ak View Post
    Murphy, I have been wondering this for some time and this was a perfect explanation. Guess I was kinda right when I kept refering to my brothers .308 as his ".300 short". Thanks again, A+
    It's a 30-06 Short

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    Yeah, realized that after I posted. "300SS"

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    Thanks for the replies. I never did the math untill now. I see that the 7mm's are based on bore diameter as well not grove as I suspected and originally stated.

    It is odd I know of 36 and 44 caliber cap and ball revolvers. So I can understand how the 44's could have been rebarreled to .432 and new cylinders made to convert to cartridge. But I have never heard of a 38 cap and ball. So it would seem for these the ~36 caliber barrel was retained and they renamed to the cartridge diameter.

    I know that names mean little to nothing, I was just hoping someone knew the exact story of how some of these differences came to exist, as there is usually a logical reason that made sense at the time.

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    Default Check the Library.

    Bandhmo: Hi there. Good question. Lost Sheep and Murphy gave you some good answers. You might try the library in Fairbanks and look in the 683 section. I've got a 2008 Gun Digest and Grennel's ABC of Reloading from the Valdez library... I'm sure that Fairbanks and the University Library has several shooting/gun/ammunition/reloading books... and they are free.

    Look for a book titled "Cartridges of the world", it has been around for years and has many listings.

    Speaking of ... the .410 gauge Shotgun is NOT a guage it is a .41 caliber/bore, yet often you stiil see/hear it called a "gauge". If it would be called correctly it would be a 67 gauge. And another thing about shotguns is that (unlike Rifle and Pistol) the smaller the gauge number -- the bigger the bore and shot ounces... example: 10 gauge is a goose gun, whereas a 20 gauge is for dove and quail.

    I sure do miss guys like Warren Page and Jack O'Conner and Col. Charles Askins and Lt. Col. Jeff Cooper. Good wisdom and almost every article you could learn something from those gents. That and some good info from the NRA junior pubs. and the older issues of The American Rifleman. {Anyone remember Mixed Bag with Jim Rikoff..? I laughed so hard the time he told of the cajun guide in the canoe in the swamps with the old muzzle-loading shotgun... Great stuff!}

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    Marketing, is a lot of it...

    325 WSM vs 8mm Rem mag

    358 Win vs 8.8mm winchester (same cartridge, WW marked early ammo boxes with both names...)

    308 Norma Mag vs 300 Win Mag vs 300 H&H vs 300 Weatherby vs 300 Savage etc

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