caliber or millimeters or what

[crackho]

I an a little confused and I hope some of you
can 'splain this to me. I was curious about
why are some firearms chambered in say 30 caliber and some firearms are chambered in say 7.62? Is this another product of Americans not being on the metric system?
http://www.ak-47.net/akcgi/confused.gif

[RogerLee]

Short answer, Yes. Long(VERY LONG) answer no (or maybe).
Lets look at the 7.62 calibre:

US-99% of the time means .308 calibre
USSR- means (mostly) .310-.311 calibre
Some countries- means .307-.312 calibre
i.e. My CZ-52 is 7.62x25mm but the bullet's measures out to be .309

Ammo, calibres, and ballistics are very hard to understand completely and are very useful for debates.
take a Winchester M-70 rifle camber in the 308 winchester round. You can shoot 308 ammo, 7.62x51 Nato, and the 7.62 CETME ammo, all three are the same size but are loaded to different pressures (in order) and some people would, for safety reasons,advise you not to shot the 308 out of a 7.62 CETME rifle.
Here is a list, of the top of my head, of all the 7.62mm camber calibres:
7.62x25mm- CZ-52 pistol
7.62x31mmR-Russian Nagant revolver
7.62x33mm- US .30 carbine
7.62x39mm- US Mini-30 rifles
7.62x39mm- Military ammo
7.62x45mm- CZ-52 Rifle
7.62x51mm- Spanish Modelo 2 rifle
7.62x51mm- US M-14, M-60 MG
7.62x54mmR- USSR M91/30 rifles
7.62x56mmR- UK Enfields rifles
7.62x57mmR- US M-1898 Krag rifles
7.62x63mm- US M1903 M1 garand rifles

Hope you get all this,
RogerLee

[Packrat]

Cartridges are named in many and curious ways. The .30-06 is a 30 calibre cartridge adopted in 1906 (to go in a 1903 rifle). The .44-40 is a .44 calibre cartridge backed by 40 gr of black powder. The .308 Winchester is a .308 cartridge that was developed by Winchester. In Europe, the metric cartridge nomenclature is standard: the .308 is the 7.62x51, and 7.62mm bullet in a case (not the cartridge) 51mm long. The .30-06 is a 7.62x63. There is no metric equivalent of the .44-40, though one could be created, since there is a standard naming device. Also, if the cartridge has a rim, the letter R is added to the case length designation, like the 7.62x54R cartridge for the Moisin-nagant rifle.

As far as bore diameter goes, this can vary between countries and even manufacturers, though generally for a given cartridge the bullet diameter will be consistant, even between countries. Thus all 7.62x51 rifles are made with a bore that accepts .308" bullets. However, sometimes manufacturers get sloppy, or dial in a little free play, so it may be .309 or .310. This is especially true of military weapons produced in war time. The only case I know of where a manufacturer deliberately chose to make a firearm that did not fit the standard cartridge that it was designed for (yes, that's a contradiction) is the Ruger Mini-30, where it was designed to shoot the 7.62x39 cartridge, which is commonly loaded with a .310 or .311 diameter bullet. However, by Bill Ruger's instructions, the barrel on the Mini-30 was made .308. The engineer designing it gave a long, tapered throat (the area between the chamber and the rifling of the barrel) so that the larger bullets could be forced down to .308 diameter without creating dangerous pressures. This is a partial cause of the notorious inaccuracy of this rifle out of the box: long throats reduct the accuracy of a barrel. Precisions rifles are made with such short throats that the bullet almost touches the rifling when it is chambered.

An amazement to me, and one tha no one has ever answered, is why bore diameters are in such odd sizes. The .44 calibre (which is actually .423, I believe) was made to take "40 balls to the pound", a common way of designating smooth-bore rifle barrel diameter, which lives on in the "bore" (british) or "gauge" (US) designations of shotguns. (A 12 ga shotgun would shoot a solid lead ball weighting 12 to the pound; a 16 ga uses a 1 oz (1 / 16 of a pound) ball. But why .308? Why .223 (or .224), the .22 calibre? Why is a .38 pistol .357", and a .45 ACP .452, while a .45 Colt is .454? There is surely a historical basis to it, but one that has been lost (or at least hidden) by the mists of time.

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Packrat

[crackho]

Thanks.
My inerests in firearms tends to run a little towards the technical side. I appreciate your sharing this with me.

[Swiss one]

Excellent posts so far..just a little addition

the 44 Mag and Spl use bullets of .429" diameter while the 44-40 uses .427" ones

[JA]

Yo crackho,
The best book I have for cartridge questions is "Cartridges of the World" by Frank C. Barnes 8th edition. You can find it at gunshows for $20 or less. It has every cartridge ever made with a pic and it's history. The comments on each cartridge will answer the question you posted. Also pics of some of the guns used to fire the cartridge. There is load data for each and at the end of every chapter there is a chart of dementions for cartridges in that chapter.
Bullet diameter and weight,cartridge lenght, case and rim diameter,etc...
If you have any questions about cartridges this is the answer book.

[JackFlash]

OK, but ya gotta figure bullet diameter versus bore diameter. And that bore diameter might be measured by lands or grooves depending on the convention at the time the caliber is developed.

Then consider that the deep lands of earlier guns have been replaced by shallow ones, and lead bullets have been replaced by jacketed.

So the ol' black powder .44 caliber loaded with lead ball at 0.44" gets refined to a shallower groove and a jacketed bullet. Not a huge jump from 0.44" to 0.429".

Same thing going on with the 38 caliber.

And you can run various bullet diameters in a bore depending on the hardness of the lead or if the bullet is jacketed. New lead alloys are very hard. Old lead ball is pretty soft.

Muzzle loaded guns use a patch -- hence a small bullet diameter for a specified bore size. Also, the muzzle loaded gun is not nearly as tight fitting on the bullet as a breech loaded gun. Lots of design flaws in running the bullet down the barrel from the muzzle.

Newer calibers seem to have more precise names. 40 S&W is 0.4000"

[alter-ego]

stick with the short answer!

[KKE]

how did a cartridge like the .38 special get
named when the closest it comes is .36?

[Poodleshooter]

The 38 special was so named due to the original bullets designed for it, an outside lubed bullet with grooves that compressed and sealed as they passed through the barrel. Those bullets were closer to .38 than the .357 bullets made and used in most ammo today. It's sort of the same reason why .429 caliber weapons were named ".44's"

[MIKE14]

So if I want to reload 7.62x39 russian I need to buy .310 bullets. not .308 What weight bullet shoots most accurately.
I have an AK-47 and an SKS Iwould like to load a round that would work well in both rifles. any recipies?


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M-14 OUT

[This message has been edited by MIKE14 (edited 11-05-2000).]

[JA]

Hornady makes a .310" 123gr soft point and Sierra makes a .311" 125gr soft point. Check www.midwayusa.com (http://www.midwayusa.com) for the best prices as they include shipping. I pull the bullets on Chinese ammo and seat Hornady bullets. Friends and I have shot several deer with this ammo and have gotten good results i.e. dead deer.
The only problem reloading for a AK rifle is that the cases get dinged up upon ejection from hitting the receiver cover. I have had no problem reloading brass fired once in a AK rifle but am leary about reloading brass fired several times from a AK rifle. As the mutiple digs could cause problems. SKS's don't ding the brass.
Also I have had slamfires using Remington primers in reloads shot in several SKS. I switched to Winchester primers to stop this. Now I use CCI military primers for reloading for SKS,AK, and any other rifle that doesn't have a spring loaded firing pin.