7.62 & .308 Win anorak question
So no this is not a thread about whether one can shoot 7.62x51 in a .308 Winchester chambered rifle or vice versa - there are plenty of threads on that topic on this site and the Falfiles.
7.62mm is 3/10 of an inch or 30 calibre in the old english, and .308 of an inch is 7.83mm.
I measured a bullet from a 7.62x51 cartridge with my vernier, and it does indeed have a maximum diameter of 7.83mm.
So my anorak question: why is 7.62mm used in the name 7.62x51 when the bullet diameter is actually 7.83mm? Or does the "7.62mm" denote some other part of the cartridge specification?
Attachment 32273
Re: 7.62 & .308 Win anorak question
It nominates the inner measure of the lands, not the outer measure of the bullet.
The 404 Jeffery has an outer measure of .423", and the 8x57 is actually 8.22mm. The 303, 7.62x39 (AK47) as well as the 7.62x54R (Druganov) measure .311".
I have never understood why the folks did this.
Re: 7.62 & .308 Win anorak question
Thank you. Some knowledgeable people on this forum. Maybe it is a military thing to confuse people. Now I am thinking that military ammunition is thus denoted with the lands measurement, and civilian ammunition is denoted with the bullet diameter.
Re: 7.62 & .308 Win anorak question
Quote:
Originally Posted by
paulnb
Thank you. Some very knowledgeable people on this forum. Maybe it is a military thing to confuse people. Now I am thinking that military ammunition is thus denoted with the lands measurement, and civilian ammunition is denoted with the bullet diameter.
There is no consistency anywhere with cartridge denominations as far as I can tell. I don't think it's true that mil is denominated with lands & civilian with bullet diameter, it's all just mixed up.............
Re: 7.62 & .308 Win anorak question
It has to do with how the bore of the rifle was measured as far as i know. The Brits measured between the grooves and the Americans measured between the lands or something along those lines. Back then when it started there was so international standard.
Re: 7.62 & .308 Win anorak question
What SJB said. Some places measured the original bore diameter, before the rifling was cut. Others measured the further measurement, after rifling was cut. It's therefore important to know what diameter your gun shoots before you grab just any bullets and load them up. Shooting .308 in a .303 won't do much (in fact it might just work), but shooting .311 in a .308 will lead to huge problems.
Re: 7.62 & .308 Win anorak question
There are 4 basic methods of caliber designation:
1. Bore diameter.
This denotes the barrel bore diameter and is smaller than the groove diameter. The numbers are a nominal diameter and will often differ from the actual bore diameter, but not by much. Military designations are often in bore diameter. Examples: 5,56mm; 7,62mm; .303 (inch), .50BMG etc. Some sporting cartridges also use this system, eg. 6mm; 6,5mm; 7mm; 8mm; .270; 300 (win Mag, BLK, H&H, Wby etc.); 404, etc. Bullet (groove) diameter may differ, the western 7,62's usually use a .308" bullet, while some east block 7.62's use a .311" bullet. The 7.62 Tokarev uses a .307 or .308" bullet.
2. Groove diameter:
Groove and bullet diameters will usually be the same. Examples: .204; .243; .308; .338; .357; .375; .416; .45; .458; 9mm; 9.3mm, etc.
3. Nominal diameter:
This number is usually neither bore nor groove diameter, but is chosen just as a name to identify the cartridge by. Examples: .222; .223; .38; .44; etc.
4. Bore or Guage:
This is usually used in shotguns. The Bore/Guage number denotes the number of perfectly spherical balls of the same diameter that can be made from a pound of pure lead. The smaller the number, the bigger the ball (and barrel). This is however not 100% consistent, as the 410 "guage" cartridge is closer to .410" diameter.
Then we get some that don't conform to any standards...
Re: 7.62 & .308 Win anorak question
Thank you all for the feedback. Seems like it is a dark art.