7.62 Nato/.308 compatibility


September 16, 2010, 10:22 PM
Hey folks, I've read various articles stating NOT to fire 7.62 Nato in a .308 chamber due to case pressure. How about firing .308 in the Nato chamber?

P.S. I may have it backwards but you get the idea of my question.

Thank you.

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September 16, 2010, 10:23 PM
You have it backwards. Don't fire 308 Win in a 7.62NATO as the 308 as a higher pressure limit.

You can shoot 7.62NATO in a 308 gun. In fact, 7.62 makes for nice light recoiling practice loads in a 308.

September 17, 2010, 12:28 AM
Please stop repeating internet nonsence as the truth.
Do everyone a favor and do a bit of research.
Real research, not what some chucklehead on the internet posted.
This has been debunked so many times it is not even funny.

7.62x51 as light recoiling practice ammo???????

7.62x51 and a 150gr .308 are nearly the same pressure wise when using the same way to get the measurement

CUP and transducer are two completely different ways to get psi and the numbers are meaningless when used against each other.

September 17, 2010, 02:43 AM
It is my understanding that there is not nearly the difference between the 7.62 NATO and the .308 Winchester that there is between the 5.56 NATO and the .223 Remington. I've always been told the two (7.62mm and .308 Win) were, for all practical purposes and intents, identical and could be used interchangeably. In doing so (I've shot several types of cheap .308 150 gr JSP hunting loads and some 168 gr .308 Win Hornady Match through my 7.62x51 NATO M1A) I've never encountered any problems concerning either safety or reliability.

September 17, 2010, 03:06 AM
My dream is that this internet nonsense will someday fade but it apparently won't.

First of all, there is NO difference between 7.62x51 and .308. Go read the explaination on the Fulton Armory website. I have personally examined and measured probably 100 different types or lots of commerical 308 and milspec 7.62 from several different countries. As with the Fulton examinations, the milspec is typically tighter tolerance than any commerical ammuntion.

Why are they the same? Because when the US Army delayed producing the 7.62 round, Winchester went ahead and marketed it commerically as the .308 Thus production of ammunition was commerically standardized as .308. So when the Army finally decided to purchase ammunition it was about (maybe) one millimeter shorter than originally envisioned as all makers refused to modify their cartridges.

There is occasionally the question of some very early rifles that are long chambers as the original specs for 7.62x51mm call for a slightly longer chamber than .308. These firearms with long chambers that will occasionally split the neck of a standard .308 cartridge? These are very early British made Enfields, I have never heard of any other gun having a problem.

Why the different pressure standards for .308 and 7.62? Milspec ammunition is intended to operate in a gas gun and needs to be regulated for the safe operation of a gas gun. Commerical ammunition can be loaded to maximum pressure because it is usually used in a bolt gun.

Gas guns need to be ran with the ammo they are calibrated for, meaning no grandpa's handloaded 220 round noses in your match M1A. Every ruined M1A I have ever seen was ruined by an idiot shooting handloaded garbage that was improperly sized, used the wrong bullet or was loaded far to hot.

September 17, 2010, 05:22 AM
I have mentioned it before about this topic being a sticky.
There have been long threads here with links and such on this all the time and the same thing keeps getting repeated.
Not that it a bad thing to ask a question, but it seems as if a sticky would clear things up for someone wanting to know.

The one in the ammo forum on the falfiles has been going on since 2001

I can see why some get turned around with CUP and SAMMI measurements as they are both gauged in psi.
No mathematical formula to convert one to the other as they are completely different ways of obtaining the pressure.

In the 1985 Lyman reloading manual they published their report on this.
They contracted HP White labs to conduct the experiment.
HP used a 30-06 as the test round.
Using a transducer(SAMMI spec) and CUP gauge(military spec) on the same round on the same firing they found....
50,000 CUP and 62,000 transducer.
The military now uses the strain gauge which is what SAMMI uses.
I believe the 7.62x51 NATO is rated at 60,500 now.
Big difference between the old CUP method.

As for gas guns and commercial ammo.. as what was previously posted and what I have said before is..
1. Headspace not exceed 1.634" SAMMI spec.
2. Keep bullet weight to 168gr loads, no hot rod loads.

Fun fact of the day.
Belgian citizens cannot own guns that use military ammo.
The FAL has 7.62 on it. Sucks for Belgian Joe.
So FN produced FAL's with .308 match on the side and a semi auto selector and now Belgian Joe can have a FAL.
Other than the markings nothing else was changed.

September 17, 2010, 05:35 AM

nothing on them but a date and maybe a letter or two NOT LC

what caught my eyes is the charge i was using was at the neck base then i found a round were the charge was slap full to the top, i checked the weight and it was correct check the oal it was OK only difference was one was a winchester the other was an old military case,

i know 223 and 556 the latter is thicker and has less room but i didn't expect the 308 case to have that much less room inside.

September 17, 2010, 05:41 AM
W.E.G. has posted his findings on ammo headspace here a few times.


September 17, 2010, 05:43 AM
7.62x51 has a thicker case.
Know what you are doing when reloading.

September 17, 2010, 08:11 AM
As stated eloquently above, they are the same round, military and civilian chambers are more or less generous. The only real interchangeability issue is for reloaders. You can't put a hot commercial .308 load into a military 7.62 case.

September 17, 2010, 09:37 AM
Off topic here, but mention was made of 5.56 being thicker and having less room than .223 brass. This is not, as a rule, true. 5.56 brass is just like any other .223 brass, it differs a bit from lot to lot. Although 5.56 has less capacity than some commercial brass, it has more capacity than other commercial brass. Always check your components when reloading and don't assume anything.

W L Johnson
September 17, 2010, 09:41 AM
Here's a link to a PDF that explains it in detail and does it clearly.

September 20, 2010, 05:42 AM
WOW, looks like I stirred up a hornets nest, sorry about that. I have done a bunch of research and always end up with conflicting answers. Having some feedback from someone who has actually done it, (thanks MTMilitiaman), makes me feel better. I was looking at some of the DPMS AR10's and noticed that some are labeled as .308 while most are in the 7.62 NATO catagory and it didn't make sense to me. Sounds like I could use either for hunting with factory ammo and plinking with military surplus.

And thanks for the .pdf W L Johnson.

W L Johnson
September 20, 2010, 08:41 AM
WOW, looks like I stirred up a hornets nest

It seems to get stirred up about every two weeks to a month. But hey, the way I look at it, better safe than sorry. But if there really was a big difference between 308 and 7.62x51 there would be a of lot blown up rifles out there, not to mention hurt people. What seems to make it worst, is that it seems alot of the time the same people time and time again repeating the same wrong info on this, on a bunch of different forums.

Oh and speaking of AR-10s
This is from ARmalite tech note #74
NOTE: ArmaLite’sŪ larger AR-10 series rifles are all chambered with 7.62 NATO
chambers. .308 Winchester (SAAMI standard) ammunition functions perfectly in the 7.62 NATO chambers.

P.S. DPMS doesn't make an AR-10, they make the LR-308 which is AR-10 "like". I'm being nit picky here but for good reason for when you buy parts you have to be careful if they are for an AR-10 (Armalite) or for a LR-308 (DPMS) because only a few parts are interchangeable between the two.

September 20, 2010, 06:32 PM
There is definitely a difference....despite some of the opinions above.

The difference is perhaps a moot point in modern rifles with modern chambers, but if you find yourself with a Spanish pre-98 Mauser with "7.62" on the barrel, like my FR-7, you'll be on the Darwin Award's short list if you run modern commercial .308Win loads through it. Not only were they designed for lower pressure (around 40K PSI, vs. 7.62NATO around 50K PSI, and .308 Win around 60K PSI), but also the metallurgy 100 years ago was nowhere near what it is today.

A fellow was killed when his gun blew up not too long ago.

Do a web search on 7.62 CETME & .308 Winchester. they are near-identical cartridges, looking at case dimensions, but the Spanish cartridge came out before NATO was around, and before NATO specs were conceived.

I mean, if they were the same, why would DPMS differentiate between the two? They should know, since they are in the business...

For further proof, use a rifle that can handle .308win (and therefore 7.62NATO) and shoot a couple of rounds of each....they'll feel different, and they'll impact different. That's also a good indicator that they are different.

September 20, 2010, 08:15 PM
desidog and others, please do some more research before posting and perpetuating this pressure nonsense.

You are simply wrong. The problem is NOT the pressure differential between the 2 loads, it's the headspace. The chamber dimensions are slightly different and you can get headspace issues with one round and not another if you are on the ragged edge. It has NOTHING to do with a pressure difference because there isn't a pressure difference.

People blow up their surplus guns because the headspace is past the NO GO and they shoot them anyway.

When that happens they LOVE to tell everyone that it was the ammo, when in fact it was simple negligence.

W L Johnson
September 20, 2010, 08:28 PM
Repeat after me
7.62x51 is NOT 50,000 psi, 7.62x51 is NOT 50,000, 7.62x51 is NOT 50,000 psi, 7.62x51 is NOT 50,000 psi

got it?

Now... Repeat after me

7.62x51 IS 50,000 CUP, 7.62x51 IS 50,000 CUP, 7.62x51 IS 50,000 CUP, 7.62x51 IS 50,000 CUP

Got it?

Now... Repeat after me

7.62x51 IS 60,200 psi, 7.62x51 IS 60,200 psi, 7.62x51 IS 60,200 psi, 7.62x51 IS 60,200 psi

Got it?

If you don't believe people here how about ARmalite?

From tech doc #74
ArmaLite’sŪ larger AR-10 series rifles are all chambered with 7.62 NATO
chambers. .308 Winchester (SAAMI standard) ammunition functions perfectly in the
7.62 NATO chambers.

September 21, 2010, 11:13 AM
Repeating something like a mantra does not confirm or rebuke anything.

When you can cite a legitimate source, then call me wrong. However, both the sources cited above indicate that there is a difference. Their point is their gun can handle either, not that the two are the same. 2 grains (or more) in case capacity and 2000PSI, while not "statistically relevant" (p.7) is still a difference.

I prefer logic: The two cases have different volumetric capacities. Two different volumes of the same powder will make for two different pressures when ignited under the same conditions.

You guys can do whatever you like, though. For me, if there is a question concerning an explosion inches away from my face...there is no question. Safety is no accident. Older guns' gas handling is more of an issue with case rupture, though. I'm not arguing that the action will blow up like a pineapple grenade.

Head-space is a separate concern; but one with plenty of merit in it's own right.

ETA: Also, .308win functioning perfectly in a 7.62 chamber is not the same statement as saying that a 7.62 chamber functions perfectly with .308win

W L Johnson
September 21, 2010, 12:18 PM
Sources were listed in my link

ANSI/SAAMI document Z299.4-1992
Does anyone have access to this right now, it's a real PITA to get of. Someone here should has it, IE reloaders.

How about proof pressure from the UK Ministry of Defence
7.62 NATO is listed in BAR which converts to 75,274 PSI which is the same as 308's proof pressure.
Note: 62,000 psi is well within proof specs. The difference between 60,200 and 62,000 is only 1,800 psi. Heck, you may get more difference than that between shooting on a cold and hot day.

And I'll quote this again from Armalite
NOTE: ArmaLite’sŪ larger AR-10 series rifles are all chambered with 7.62 NATO
chambers. .308 Winchester (SAAMI standard) ammunition functions perfectly in the 7.62 NATO chambers.

September 21, 2010, 12:49 PM
I prefer logic: The two cases have different volumetric capacities. Two different volumes of the same powder will make for two different pressures when ignited under the same conditions.

as i said some were up above.

i had some mil 308 get in with some commercial and when the powder drooped i noticed right off something was off. the case was full to the top, i could tap it and it would settle somewhat but case in point it would have been a compressed load.

yes i measured the powder and it was still right on and both cases were same OAL,
i have run into this in some LC 223 but not as extrema as this was.

i was also not loading at the max amount if i was powder would have spilled over the top.

i didn't expect the military case to have that much less room inside, could have been an odd ball few cases but never the less it was too full for me.

another good reason to separate all your cases to brand. my .02 take it or leave it. just an FYI.

LIKE 223 AND 556 thee different but not enough for me to worry about as long as my gun says 223 or 556 i feel im good to go on the pressure side. but still separate them.just so they will be the same in the batch loaded.

October 21, 2010, 03:53 PM
I just bought 500 rounds of Tula 308-7.62x51 for my Socom II and Remington, Did I just FU?

October 21, 2010, 04:03 PM
Is that the steel jacketed stuff? That's for another thread.

Average Joe
October 21, 2010, 08:01 PM
Blacky, its fine . Shoot it and enjoy .

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