So what you are saying is that I should attempt to buy guns chambered for 5.56 and 7.62 and shoot commercially available 223 and 308 (respectively) through them as opposed to buying .223 and .308 and risk only having 5.56 and 7.62 rounds available at a later time?
[My wording may be a bit off here, but please read the 'heart' of the question... as it is, actually, a 'serious' question.]
If you want to shoot 5.56 or .223 Remington. Get a gun stamped 5.56 (most ARS are stamped Both....
There has been some discussion on .308 vs 7.62x51. Technically those are not the same cartridge either. IIRC .308 uses a thicker case wall vs. a 7.62x 51 uses a thinner case wall. Therefore IIRC compatabiblity is reversed for the .308. I.E. in .308 Win chambered guns you can shoot either one. I might have this backwards
In 7.62's you can only shoot 7.62x51. Some one will probably say (it doesn't matter).
However, when I was at Virginia Military Institute we did a US military historical shoot. We had about 3 M14's (yes you heard correctly M14's NOT M1A's). All of them had case separations occur inside the chambers. IIRC we where shooting .308.
No, Virginia, .308 Win. and 7.62mm NATO Are Not Identical
At distressingly frequent intervals, someone can always be be counted on to pop up on an Internet Forum somewhere and ask Is the .308 Win round different than 7.62x51 NATO?. There follows a diluge of responses explaining with different degrees of success, this well-documented issue. So let this serve as a "mini-FAQ" on the subject.
The .308 Winchester and the 7.62mm NATO (nee T-65) cartridges are not the same1, nor should they be considered interchangeable despite apparently identical external dimensions… the chamber drawings are in fact different.
But as Clint McKee and Walter Kuleck of Fulton Armory note on their "award-winning" website:
They are the same, 'cause nobody makes 7.62mm (NATO) ammo that isn't to the .308 "headspace" dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.
MAP: 62,000 psi
MPSM: 66,000 psi
Minimum Proof Pressure: 83,000 psi
Maximum Proof Pressure: 89,000 psi
7.62 x 51mm NATO
Maximum: 50,000 psi
Proof pressure: 67,500 psi
Sources: .308 Winchester data from ANSI/SAAMI document Z299.4-1992, Pressure and Velocity, Centerfire Rifle Sporting Ammunition
7.62 x 51mm NATO headspace data from Jerry Kuhnhausen's M1/M1A shop manual.
Pressure data from TM 43-001-27: Army Ammunition Data Sheets Small Caliber Ammunition
According to Ken at Clymer Tools
, noted maker of headspace gauges, the problem isn't the round itself, it's the headspacing.
A 7.62 NATO Go
gauge is .003-inch longer than a .308 Winchester Go
gauge. The 7.62 NATO NoGo
is also longer, to the tune of .004-inch. It's entirely possible to chamber and have an accident with a .308 Winchester round in a rifle that would be safe for 7.62 X 51mm. A chamber in 7.62 that could barely close on a 7.62 NoGo
could swallow a .308 Field gauge. Add to this the fact that .308 Winchester brass, being of commercial manufacture, is much thinner than that of the 7.62 NATO, and expands alot more, could possibly lead to casehead separation.
And just when we thought that we had this 7.62mm NATO stuff down pretty pat, along comes Adam Firestone at Cruffler.com
with his taste for the arcane, who makes a compelling brief that much of what many thought they "knew," was all wrong! An excerpt:
Many shooters are aware of the differences between the dimensionally similar 7.62mm NATO cartridge and the .308 Winchester. What most are not aware of is that all cartridges called "7.62mm NATO" are not created equal, and that there is significant variation, both dimensionally and ballistically, between 7.62mm NATO cartridges as manufactured by different countries, and even between such cartridges as manufactured by different arsenals within the same country. As a result, the terms "NATO spec" or "NATO standard," which imply that all "NATO" cartridges are the same or to indicate the fitness of given 7.62x51mm ammunition for a specific use, are misleading.