7.62 x 51 Nato out of a .308

[Nowhere Man]

From what I've read, it's OK to shoot 7.62 Nato out of a .308 Winchester.(?)

Would the combination be any less/more accurate than using .308?


Dave

 

[jonnyc]

Perfectly ok, 7.62x51 and .308W are the same round. Lots of factors contribute to accuracy, you'll probably have to experiment a bit and see.

 

[docnyt]

It's like the 5.56 versus .223 debate.

EDIT: meant .223

 

[Nowhere Man]

OK Thanks.


Dave

 

[Motega]

it's not the same round from what I've read- case pressures are different from what I understand. It's "OK" to shoot a 7.62 from a .308 but from what I understand when pushing a .308 to it's practical limits yu shouldn't fire it from a rifle specifically designed for 7.62. I would think most factory loaded ammo wouldn't be hot enough to make a difference but on the off chance someone is handed a boxful of hot handloads, it could be a problem. Is this accurate, or are factory .308's equally dicey?

 

[TexasRifleman]

OK I'm gonna post then lock this one before any more misinformation gets posted. Search is your friend, there are untold numbers of threads on this topic here and other gun forums.

x51 and .308 do NOT have different pressures. The pressures are measured using different techniques, thats why you see different numbers like 50,000 vs 65,000 etc. They are NOT both measured in PSI. One is PSI one is CUP. They are not interchangeable. Google is your friend for more info on this. CUP stands for "Copper Units of Pressure".

What matters most is headspacing, especially in milsurp style semi auto rifles. There are slight differences in chamber dimensions and brass thickness between commercial .308 and x51. Excessive headspace in a rifle designed for x51 can cause case ruptures when using what is (usually) thinner brass found in commercial .308. That makes it look like "overpressure" but what it really is, is a failure to properly contain the pressure. NATO brass tends to be thicker and is sometimes able to withstand a bit more of this pressure but the same thing can happen with NATO brass.

You usually find headspaces that are at or exceeding the limits on milsurp rifles, that's why shooting .308 in a rifle designed for x51 requires that you check the headspace.

Bottom line is that as a general rule .308 and x51 are interchangeable as long as you are shooting them in a rifle that is safe to begin with. That means checking the headspace.

For the specific question here of shooting x51 in a .308 chamber, that's a non issue pretty much. The problem, if there really is even a problem, is shooting 308 in an x51 chamber.

Good short writeup from Walk Kuleck at Fulton Armory on this topic:

They are not the same.

They are the same.

They are not the same, 'cause the .308 Win was released by Winchester several years before the Army standarized the T64E3 as the 7.62MM. You'll get an endless discussion of pressure specs, endless because SAAMI and the Ordnance Dep't measured pressure in different, unrelateable ways. Howver, the chamber drawings are different.

They are the same, 'cause nobody (and Clint's been looking for many years!) makes 7.62MM ammo that isn't to the .308 "headspace" dimension spec. So 7.62MM ammo fits nicely into .308 chambers, as a rule.

But in some 7.62MM rifles the chambers are long (to the 7.62MM military spec), notably the Navy Garands with 7.62MM barrels. Thus, using commercial ammo in such a rifle is not a good idea; you need stronger brass. Use military ammo or the best commercial only, e.g., Federal Gold Medal Match.

Most of the time it's a distinction without a difference. But if you intend to shoot .308 commercial in a military arm chambered for 7.62MM, first check the headspace with .308 commercial gauges first. You may get a surprise.

Best regards,

Walt Kuleck
Fulton Armory webmaster

More from Walt on this, since it keeps coming up.

Jerry Kuhnhausen, in his classic Shop Manual (available from Fulton Armory; see the M1 Rifle Parts & Accessories or M14 Rifle Parts and Accessories Pages under Books) has published a somewhat controversial recommendation concerning .308 Winchester and 7.62x51mm NATO ammo, headspace & chambers. I broached the subject with him some months ago. He had his plate full, so we decided to chat on this in the future. When we do I'll report the results of our conversation.

I completely agree with Jerry that if you have a chamber with headspace much in excess of 1.636 (say, 1.638, SAAMI field reject), you must use only U.S. or NATO Mil Spec Ammo (always marked 7.62mm & with a cross enclosed by a circle) since the NATO mil spec calls for a far more "robust" brass case than often found in commercial (read .308 Winchester) cartridges. It is precisely why Lake City brass is so highly sought. Lake City brass is Nato spec and reloadable (most NATO is not reloadable, rather it is Berdan primed). Indeed, cheaper commercial ammo can fail at the 1.638 headspace (e.g., UMC) in an M14/M1 Garand. Many military gas guns (e.g., M14 Rifles & M60 Machine guns) run wildly long headspace by commercial (SAAMI) standards (U.S. Military field reject limit for the M60 & M14 is 1.6455, nearly 16 thousandths beyond commercial (SAAMI) GO, & nearly 8 thousandths beyond commercial (SAAMI) field reject limit!).

I also agree that 1.631-1.632 is a near perfect headspace for an M14/M1A or M1 Garand chambered in .308 Winchester. But I think that it also near perfect for 7.62mm NATO!

I have measured many, many types/manufacturers of commercial and NATO ammo via cartridge "headspace" gauges as well as "in rifle" checks. If anything, I have found various Nato ammo to be in much tighter headspace/chamber compliance than commercial ammo. Indeed, sometimes commercial ammo can not be chambered "by hand" in an M14/M1A with, say, 1.631 headspace (bolt will not close completely by gentle hand manipulation on a stripped bolt, although it will close & function when chambered by the force of the rifle's loading inertia), though I have never seen this with NATO spec ammo. I.e., if anything, NATO ammo seems to hold at the minimum SAAMI cartridge headspace of 1.629-1.630, better than some commercial ammo!

So, why set a very long 1.636 headspace in an M14/M1A or M1 Garand? It probably is the conflict mentioned above. Military headspace gauges say one thing, SAAMI headspace gauges say something else, as do the spec's/compliance covering ammo. In a court of law, who will prevail? I think Kuhnhausen gave all those who do this work a safe way out. However, I believe it not in your, or your rifle's, best interest. Whether you have a NATO chambered barrel (M14/M1 Garand G.I. ".308 Win."/7.62mm NATO barrels all have NATO chambers), or a .308 Winchester chamber, keep the headspace within SAAMI limits (1.630 GO, 1.634 NO GO, 1.638 FIELD REJECT). This subject is a bit confusing, and for me difficult to explain in a one way conversation!