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Author Topic: why caliber and not mm?
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posted 11-06-2000 08:05 PM       Edit/Delete Post   Reply With Quote
My foolish question (I don't know much about guns)

Why are some bullet diameters measured in caliber while some in millimeters?


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Andy Bush
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posted 11-06-2000 08:17 PM     Profile for Andy Bush   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
TC

The term for bullet (or bore) diameter is 'caliber'. It is usually measured in inches or millimeters.

Andy


Posts: 595 | From: St Louis, Mo | Registered: Sep 1999  |  IP: Logged
Sammer
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posted 11-07-2000 02:01 AM     Profile for Sammer   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Before they started using the metric system, they measured the diameter of the bore in inches.

For example a 0.50 Calibre MG has a 0.5 inch thick (internal diameter) barrel.

-Sammer


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Paul Morrison
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posted 11-07-2000 09:37 AM     Profile for Paul Morrison   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
.50 Cal is aka 12.7 mm
Posts: 1143 | From: Ontario | Registered: Sep 1999  |  IP: Logged
Skoonj
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posted 11-09-2000 05:46 AM     Profile for Skoonj   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
There is one other use of caliber. In naval guns caliber refers to the length of the gun. In other words, the Iowa class battleships have 16"/50 caliber main gun. That means the width (diameter) of the bore is 16 inches. The length of the barrel is 50 times the diameter of the bore. Multiply 16" times 50, and you come up with the length of the gun in inches. That's 800 inches.

Skoonj

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Posts: 541 | From: Naples, Florida, United States | Registered: Sep 1999  |  IP: Logged
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posted 11-10-2000 11:16 PM       Edit/Delete Post   Reply With Quote
Thank you.
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Rosco
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posted 11-11-2000 12:19 AM     Profile for Rosco   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
What Skoonj said is also true of land based atillery and cannons as well.

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"You, Out of the gene pool!!!"


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Tailspin
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posted 11-13-2000 05:29 PM     Profile for Tailspin   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Ahhh...but all "calibers" are not true bore diameters. The .44mag. is actually .429in dia. and the .38special is actually .357in. bore dia. The .380auto is .355in. And there's more. I guess the quaint old English measuring system is to blame.

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Joke 'em if they can't take a....


Posts: 1895 | From: Metropolis USA | Registered: Sep 1999  |  IP: Logged
Rick.50cal
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posted 11-14-2000 02:58 AM     Profile for Rick.50cal     Send New Private Message   Edit/Delete Post   Reply With Quote

There's actually a bit of a fudge factor there too, to the tune of about .002 to .004 inch, since reloaders can sort of interchange between 9mm bullets, .38spl and .357m. I suspect that this works well in some barrels but not others, due to shape of rifling and other factors. I suspect that at .004 and larger gaps, gas blowby would reduce your velocity.

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Rick.50cal


Posts: 520 | From: Vancouver, BC, Canada | Registered: Sep 1999  |  IP: Logged
tony draper
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posted 11-14-2000 03:29 AM     Profile for tony draper   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
I believe bore meant something slightly different, 12 bore was something to do with the number of balls that fit a barrel of a certain size, incidently i had a 410 shotgun in my youth and this quite happily fired .455 eley pistol cartridges, mind you they eventualy made a mess of the barrel.
Cannon calibre was also messured by the weight of the ball that would fit the barrel.

Posts: 1280 | From: england | Registered: Oct 1999  |  IP: Logged
Tailspin
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posted 11-16-2000 07:00 PM     Profile for Tailspin   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
The original shotgun gauge was the amount of lead balls the diameter of the bore it took to weigh a pound. Thus if it took 12 lead balls of a given bore diameter...the bore was a 12 gauge. 20 gauge took 20 balls of bore diameter etc... The .410 shotgun as the decimal suggests is .410in in diameter. Being a smoothbore there is some lee-way in the size of a slug that can pass through it.
Slickster is right also. .38spl. slugs can be .357 or .358 and a 9mm(.354/355in) bullet will shoot in a .357in barrel...Most of the time. Due to variations such as mentioned here and changes in standards over the past 100+ years,it is never 100% safe to shoot any size projectile in a firearm not specifically intended for that firearm.

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Joke 'em if they can't take a....

[This message has been edited by Tailspin (edited 11-16-2000).]


Posts: 1895 | From: Metropolis USA | Registered: Sep 1999  |  IP: Logged
Sammer
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posted 11-17-2000 03:03 AM     Profile for Sammer   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Also, .223 is not 5.56mm!

-Sammer


Posts: 137 | From: Singapore | Registered: Sep 1999  |  IP: Logged
Slickster
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posted 11-17-2000 12:52 PM     Profile for Slickster   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Anybody that is familiar with the MA2 50cal machine gun knows about the "head spacing". Browning actually engineered an adjustable chamber into the thing, so that one could fire ammo from all over the world, some possibly just slightly different in size. You have to set the head spacing every time you reassemble the weapon after cleaning. If you don't know how, you're out of luck. It was a nice idea, but now is just an extra, time consuming step in reassembly.

I think the 30 cal browning had the same deal, but I could be wrong.

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Rick "Slick" Land


Posts: 551 | From: Fayetteville, AR, USA | Registered: Sep 1999  |  IP: Logged
Rick.50cal
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posted 11-17-2000 02:24 PM     Profile for Rick.50cal     Send New Private Message   Edit/Delete Post   Reply With Quote
Slickster, that is true for almost all M2's but not for a handfull of new ones, as they now come with a "QD kit" enabling the easy and ultra fast barrel changes without having to screw it on, or checking headspacing. I'm not too sure how you would fire lower quality ammo in this new QD, but since most modern western .50 ammo is top quality, this is no longer the huge problem it was. When I was in Yugoslavia, we used API-T, which is similar or a copy of the Raufoss round, lots of power!

Headspacing, if not done correctly, will either result in no cycling of the action, or it will blow up partially out of battery, and on a .50 that means a face full of steel from the feed cover.

I have used both the original and new QD versions quite a lot. Too bad I live in Canada, or I might buy one! They are really that much fun!

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Rick.50cal


Posts: 520 | From: Vancouver, BC, Canada | Registered: Sep 1999  |  IP: Logged
dschin
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posted 11-18-2000 11:10 PM     Profile for dschin   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Skoonj/Rosco: Was there some reason for proportioning bore diameter to barrel length?
And were the old English "pounder" designations indicative of the weight of the projectile?

Posts: 287 | From: Madison WI USA | Registered: Aug 2000  |  IP: Logged
Slickster
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posted 11-20-2000 10:48 AM     Profile for Slickster   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Vellly intelesting, Rick. I've fooled about with the .50 "Ma Deuece" as well, and it is a gas to fire. The thing is just SO much more powerful than a .30 cal. The head spacing is a nuisance to fool with. I didn't know there were some without it, and I must say, about time.

The thing fires a round that weighs, from memory now, about 750 grains? Contrast that with the 150-200 grains in the average .30 rounds. And, fires them at a higher muzzle velocity in most cases.

My Pop flew the B-26 in Korea. In the solid nosed versions there was usually 18 .50's that could be brought to bear on a target (8 in the nose, 3 in each of the wings, and the top and bottom turret locked forward). This wouldn't kill a tank, but it would knock off every piece of equipment mounted externally, rendering it hors de combat.

Interestingly, he says that one could kill a tank, if the ground was frozen, by aiming in front of the tank, getting the ricochets to go up into the belly. He never did it, but that was the conventional wisdom.

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Rick "Slick" Land


Posts: 551 | From: Fayetteville, AR, USA | Registered: Sep 1999  |  IP: Logged
Rick.50cal
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posted 11-21-2000 01:59 AM     Profile for Rick.50cal     Send New Private Message   Edit/Delete Post   Reply With Quote
Hmm, interesting.... I would venture that the ground may not have to be frozen to do that, as I have seen lots of ammo types ricochet off of supposedly "soft" ground. But...... 18?!?! As in 1, 8 ? as in 9+9 ? Gives new meaning to the term Gunship!

By the way, the QD kits were invented by FN Belgium, and licence production is being done in, USA and UK, perhaps others. Not all new current .50's have this kit, either, since many armies may not be in the market for a large buy, but more of "we need five more for the jeeps, get the same kind". Armies buying the QD version would need to change an entire brigade all at once, or you would find training and logistics problems, but many would not be willing to introduce a change at extra costs, even if it means a better system.

BTW: the guns your dad flew with spit out a total of 225 shells per SECOND!!! By comparison, the A-10's gatling can only do 70 shells at maximum rpm.

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Rick.50cal


Posts: 520 | From: Vancouver, BC, Canada | Registered: Sep 1999  |  IP: Logged
Slickster
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posted 11-21-2000 12:42 PM     Profile for Slickster   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Yep. Eighteen. There were two versions of the Douglas A/B-26 Invader. A "solid nose" version with 8 .50's in the nose, with a second crewman to mind them. He took off next to the pilot, and was the armament guy. The plane either had 3 integral .50's in each of the wings, or could carry gun packs added to the underside. The two turrets, dorsal and belly, were manned by one gunner with a periscope type sight, not unlike the remote system on a B-29. By all acounts, the system worked well.

The two turrets could be locked forward, out of control of the gunner, to add to the weight of the fire. Pop said this wasn't done much, as it took the guns out of the hands of the guy, and he didn't like that.

Another reason was that after a run on a target (at night) if any return fire was recieved, the rear gunner would engage the enemy crew until the Pilot could get eyeballs on. Then, the full weight would be brought to bear.

Another cool thing was that the top turret ,if locked forward, had a 1 degree upward loft to the guns. The pilot would use this to walk the top guns onto the target, then fire the other guns. Pop said the twin .50's going off right over his head at night was spectacular.

There was also a "glass nosed" version, with a bombardier navigator position in the front. Obviously, these planes lacked the nose armament. All versions could carry a large internal bomb load, and rockets, if available, as well as the gun armament.

They served in WW2, Korea, Viet-Nam, and still today in various fire fighting squadrons.

Any arguments about the best medium bomber etc have to at least consider this outstanding plane.

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Rick "Slick" Land


Posts: 551 | From: Fayetteville, AR, USA | Registered: Sep 1999  |  IP: Logged

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