7.62x51 vs .308


February 28, 2008, 07:51 PM
Hopefully this will be my last question to clairify things. Can you shoot .308 in a 7.62x51 chamber? Can you shoot 7.62x51 in a .308 chamber? The reason I am getting into the topic is I was trying to streamline my firearms into a few easily stockpileable calibers so it would be cheap to shoot them. I have a M1A Loaded, CETME stamped .308, and a DPMS LR-308 on order. The DPMS and M1A are high dollar firearms and I don't want to damage them by feeding them the wrong ammo. I understand the 7.62x51 is slightly longer w/ a thicker case and that the .308 has higher pressures I just want to know if they are interchangeable. Also why does almost every ad on a firearm in the caliber say 7.62x51(.308) if they are not truely the same thing?

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February 28, 2008, 07:56 PM
As I understand it the .308 Winchester is safe in the 7.62X51 but the 7.62X51 may not be safe in a .308 Winchester chamber (same as .223 Remington vs 5.56X45).

February 28, 2008, 07:59 PM
For all intents and purposes, they're more or less the same thing.

What you really need to watch for is heavy bullets and slow burning powders. Stick to 150-170 grains and below, and you should be good. Avoid stuff like the "Hornady Light Magnum" stuff - they get the velocity with a compressed charge of slow powder.

General Geoff
February 28, 2008, 08:34 PM
As I understand it the .308 Winchester is safe in the 7.62X51 but the 7.62X51 may not be safe in a .308 Winchester chamber (same as .223 Remington vs 5.56X45)

It's the opposite; 7.62x51mm is fine in a .308 chambered rifle; .308, however, may not be fine in a 7.62x51mm rifle.

The external case dimensions of the cartridges are identical; the internal dimensions are very nearly so. The main difference stems from the fact that 7.62x51 brass is thicker and stronger; the go/no-go chamber dimension tolerance specs are looser in 7.62mm chambers because of that. So a very loose 7.62mm chamber may be "safe" to fire 7.62 cartridges, but not thinner-walled .308. A tightly chambered 7.62mm rifle will handle both cartridges just fine, and any .308 that's passed factory chamber spec has a tight enough chamber for both.

February 28, 2008, 08:36 PM
Geoff for the win.

February 28, 2008, 08:38 PM
I had SEI build my M14s with M-118 LR chambers so that I don't have to worry about whether it's .308 or 7.62m :cool:

February 28, 2008, 08:42 PM
Found this on the Fulton Armory site. Some things are never simple.

What's the Difference between .308 Winchester & 7.62x51mm NATO?
by Clint McKee and Walt Kuleck

dumb question i alway thought these 2 ammos where interchangeable but some have told me otherwise whats the story??? jim

Hi, Jim,

This is a perennial topic, kinda like ".45 vs. 9mm" or "Best Guns & Loads for Deer."

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

Clint, What's the difference between .308 Winchester & 7.62x51mm NATO?

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!

Clint McKee

February 28, 2008, 09:56 PM
For all intents and purposes, they're more or less the same thing.

No problem interchanging them, other than obvious platform restrictions such as port pressure caused by a slower burn rate powder. Depending upon an individual rifle's 7.62x51 chamber dimensions, brass life of .308 Win ammo fired in a 7.62x51 chamber may be short.


February 29, 2008, 12:46 AM
Check the 7.62 x 51 chamber with a 308 commercial guage, if it's go, it should be fine as long as someone suggested don't use heavy bullets and slow burning powders in a military semiauto.

February 29, 2008, 09:44 AM
I shoot commercial .308 in my 7.62 FAL, but my headspacing is good and I haven't (yet) shot anything heavier than a 150gr bullet.

February 29, 2008, 10:25 AM
Since you have a M-1A I would be more worried about the powder burn rate than if it's a 308 or 7.62 Nato. Any ol' 308 isn't going to work without bending something.

March 20, 2008, 02:52 AM
I called Springfield Armory customer service today and they said that .308 would be just fine in my M1A standard. I will now be buying .308 in bulk because my other 2 rifles are .308.

March 20, 2008, 04:35 AM
CETME's fluted chambers were designed to fire the thicker military brass and have a reputation for tearing the case head off of thinner commercial brass every once in a while.

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