.308 vs 7.62 NATO

ISCS Yoda · #1 10-21-2014, 03:31 PM

This is the "and" from my .223/5.56 question....same question, actually....

As I recall, if your rifle is marked 7.62 NATO you're good to go with either .308 or 7.62 but if your rifle is marked .308 you should stick to .308. I hope it's not the reverse but my memory ain't that great.

Feel free to discuss semi-auto platforms like the M1A - but my question is, what about a typical bolt action rifle - if your bolt gun is marked .308 does it matter nearly as much as in a mil-spec semi-auto type of rifle?

This is not a new subject and I have discussed it with people before. My problem is, I can't remember!

Thanks.

***GRJ***

TenTea · #2 10-21-2014, 03:34 PM

Let's ask Clint & Walt.

Fulton Armory: What's the Difference between .308 Winchester & 7.62x51mm NATO?

Summary from arfcom.

Quote:

7.62 and .308 differences summed up:

7.62 has a longer permissible headspace for reliability in full auto weapons.
7.62 has thicker brass
7.62 is loaded to lower pressure (compare CIP specs to NATO specs since they use the same measurement standard)

Because the 7.62 potentially has a long chamber, the brass is made thicker and pressure kept lower to keep from rupturing cases. Firing a .308 round with higher pressure and thinner brass in a chamber with excess headspace (by .308 standards) is asking to blow up a case. Might not hurt the rifle but will probably scare the **** out of the shooter when he gets a face full of hot gas.

If a rifle marked 7.62 has the chamber checked and it falls within .308 headspace dimensions, firing .308 in it should be OK. Be cognizant of gas volume and pressure with piston operated rifles as too much of either can damage the operating system.

ISCS Yoda · #3 10-21-2014, 03:43 PM

Nice, TenTea, I like it.

Quote:

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.

There's the key, right there, and it does trigger my memory banks. The warnings I got were always about shooting commercial .308 in a 7.62 chambered M1A. I was NEVER warned to avoid shooting mil-spec 7.62 NATO ammunition in my .308 bolt gun.

I'll be interested to see if the .223/5.56 discussion goes the same way.

***GRJ***

TenTea · #4 10-21-2014, 03:45 PM

Quote:

Originally Posted by ISCS Yoda

I'll be interested to see if the .223/5.56 discussion goes the same way.

***GRJ***

If your weapon is marked 5.56mm you can take on all comers.
If marked .223 then stick to commercial, I suspect would be prudent unless gauge verified.

Fishinfool · #5 10-21-2014, 03:51 PM

Good info posted by TenTea. I'll ad that NATO ammo uses a slightly harder primer cup to avoid slam fires in semi / full auto's with floating firing pins. That said, I have fired thousands of reloads using regular commercial primers in CETME's, FAL's, M1a's, AR-10's, and HK-91's without this issue being a problem. No case separation issues either, when using regular .308 brass. It is always a good idea to check the chamber on a mil surplus rifle before firing, as the possibility of a "sloppy" chamber does exist. The above issues should be non-issues when using either ammo in a commercial bolt action rifle, with standard .308 chambers.

Larry

hoc9sw · #6 10-21-2014, 04:15 PM

I didn't go the scientific route. I just asked Ruger about my .308.

I have a Gunsite Scout .308 Win rifle. I have been given conflicting information about ammunition. Will this rifle use 7.62x51 cartridges without problem?

Thank you.

Response:
7.62 x 51 NATO can be fired in any and all M77’s and Hawkeyes, Scout Rifle and the American chambered for 308. Military surplus ammunition can vary greatly in its quality and consistency.

If you need further information, please visit our website at www****ger.com or contact us at:

LVSteve · #7 10-21-2014, 09:59 PM

Oh no, not this again.

The 7.62 NATO standard does allow for longer headspace than the SAAMI .308 standard. However, this applies TO THE WEAPON. Reloaded .308 that is getting thin may go "pop" when used in a 7.62 NATO gun with a max length chamber.

Also, I defy anyone to tell me that they have measured the cases of .308 and 7.62 NATO ammo and found any difference in the length or shoulder position. As stated above, the only difference is in the brass thickness at the web and the ultimate case capacity.

I had a bunch of cases sectioned and we came to the conclusion that the commercial suppliers all seem to be using 7.62 NATO sized brass. Think about it, if you are producing for the civilian and military markets, do you really want to use different sizes of brass for essentially the same ammo?

Then there is the pressure question. .308 is rated to MARGINALLY higher than 7.62 NATO when measured USING THE SAME METHOD. Please don't requote the old saw about 7.62 NATO being 52,000 psi CUP and thus much less than .308 at 62,000 PSI. First, there is no such measurement as "PSI CUP". Second, the measurement systems are totally different and all but impossible to relate.

I believe the latest CIP standard is 60,000 for 7.62 NATO and 62,000 for .308, i.e., less than 5%. You'll see more variation in pressure than that just leaving your ammo in the sun on an otherwise cold day.

One more big difference between .308 and 7.62 NATOthat is important for the milsurp semi-auto guys. 7.62 NATO ammo has a medium speed burn powder suitable for automatic and semi weapons. MANY types of .308 use double based powders with long burn times and long pressure curves. These are unsuitable for many milsurp semi-autos, even those with adjustable gas systems. I own a FAL, and I've been there, done that, stopped just before I got brass stuck in the chamber with the case head elsewhere.