PvtPyle can give us a more professional and authoritative response, but the short version is 'same deal'.

Military ammo is a little hotter, military chambers have a little more freebore and so on.  Therefore, shoot .308 in 7.62 chambers without much reservation, but not so much recommended the other way round.

PvtPyle can give us a more professional and authoritative response, but the short version is 'same deal'.

Military ammo is a little hotter, military chambers have a little more freebore and so on.  Therefore, shoot .308 in 7.62 chambers without much reservation, but not so much recommended the other way round.

With .308 vs. 7.62x51 it's actually the other way around.  .308 Winchester is hotter.  So firing milspec ammo in a consumer firearm should be fine.  Firing consumer ammo in a milsurp is dangerous.

From this article:  http://www.surplusrifle.com/shooting2006/308vs762nato/index.asp

In terms of pressure, there is a wide (very wide) gap between the 7.62 NATO and the .308 Winchester.  Here at Surplusrifle.com, we recommend in the strongest possible terms that you do not fire factory .308 Winchester ammunition in any Mil-Surp rifle chambered for the 7.62 NATO round.

Everything else I've read on it backs this up.  DO NOT fire .308 factory ammo in a 7.62 NATO chambered rifle!


-T.

As noted above Commercial 308 is hotter by a bit.  Most(not all) modern 7.62 battle rifles will handle either.  Some of the older models will have trouble with it.

Well, the time may come where 7.62 x 51, surplus or otherwise, may not be available. In fact, we had a form of that for almost a year already. What will you do, or better, what will I do, since I have half a dozen of that caliber rifle.

The difference isn't the size of the cartridge, it's the chamber of the particular rifle. 7.65 x 51, has a thicker brass case and the shoulder is often "annealed" so that the cartridge will tolerate more headspace. Thus a particular rifle will be useful longer. The first thing to do is check an older military rifle for 308 headspace, using a 308 guage. This is a good idea anyway, when you happen to buy a surplus rifle. At some pont you may want to handload, although some munufacturers don't recommend it. If your military rifle is on the long side of headspace, the brass is going to grow to fit the chamber. I the same way, my MAS 49/56, converted to 308, functions well, but from what I hear, will distort the brass to make it unusable for other 30 caliber rifles. It's a pain but segregating brass may be necessary. Anyway, if at some point you have to use 308, and it may come to that, use lighter loads and lighter bullets. The FMJBT from PRVI Partisan seems to be what would work, but I haven't fired it in those rifles I'm not sure about. It is also as vulnerable as any other imported ammunition to import bans, so that may not be a viable option either. So, since there is Lithuanian, German, and South African 7.62 x 51 available now, the best option is to stock up now, and avoid the hassle later. There is always white box Winchester, but how easy would it be to run THAT out, or for the government to persuade them not to sell it? I only worry about the MAS 49/56 and the Argentine FN-49, and not my FAL or M1-A. I had the FAL checked, and the headspace is good, in fact, at the shorter end of headspace.

Looking at my Saiga, it has both markings on the receiver. ".308 Win." on top of "7,62x51".

I've never shot commercial .308 through it, but I'm guessing it would be ok. Any insights on receivers having both calibers marked on them?

Perhaps this will help.

http://www.fulton-armory.com/308.htm

I would again apear that shooting 308 in a rifle chambered in 7.62 is probably not a good idea with out checking the head space first.

I agree all are different, and pressures deal with both chamber
dimentions and brass thickness first, as it is the start point before
propellant and bullet length is considered to contribute to chamber
pressures.   I have a 308 Garand Match, and a Reminton 788, and
a Savage lever.   Used both commercial and military in all three.
No pressure problems or indications of incompatibity in ammo use.
I do reserve ammo that duplicates the military in the Garand, as
the semi auto is designed to operate in and around certain time/
pressure rates to prevent battering.   I suspect with an adjust-
ble gas cylinder plug you could tweak other loadings.
   Bottom line is I use care with the gas operated rifle as to what
goes into it.   The other two will interchange, or all three with the
military loads without concernment on my part.   Heavy bullets and
slow powder like the 30-06 in the Garand I avoid in the 7.62 or 308
also.   Not because of chamber pressure, but componets that are not
in the same area of operation of design.

It doesn't make sense to me why a military load would be 12,000 PSI less than a civilian manufactured load.  Usually military loads are hotter so that they can operate in machineguns.  I tend to agree with the 'rumor' that one or the other was measured in CUP and marked as PSI or vice versa.  I have been told that according to Lyman, in their 1992 reloading manuel, that in fact the pressure numbers are missmarked on NATO loads (7.62x51).

Does anyone agree or have any sources to support this?  I am going to get a hold of Lyman and ask.

1. There's no rumor about the fact that NATO and SAAMI measure pressure differently. It's even conceivable that you could have two rounds loaded with powders producing wildly different pressure curves and SAAMI and NATO testing would disagree about which one produced more pressure.

2. There have been plenty of reliable machineguns chambered for rounds with a lot lower maximum pressures than the 7.62x51 NATO.

3. At the time the 7.62x51 NATO was introduced, a lot of the NATO members were looking at having to redesign their weapons to use the new cartridge. Many of those weapons were originally built for much less robust rounds than the 7.62x51 NATO they were being pressured to adopt (such as the .280 British and 7.62x51 CETME).

Wait a minute, look at this:
http://www.smellysmleshooters.net/ammopressure.htm
SAAMI doesn't list .308 as being dangerous in 7.62 chambered arms:
http://www.saami.org/Unsafe_Combinations.cfm

Here's another good discussion to take a look at:
http://outdoorsbest.zeroforum.com/zerothread?id=87590
In one or two of the posts in this discussion it is mentioned that the 50,000 PSI of 7.62 NATO was taken using the old copper crusher method, and therefore is actually 50,000 CUP; compared the the 52,000 CUP of .308 Win.  Not much of a difference:
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=773436

Some good points that I have found that have been made were, "There's no warning on Win. .308 ammo boxes" and "all U.S. reloading manuals list .308 and 7.62 NATO as being identical.  As for the warning on Win. .308 ammo boxes, it is a good point; I am sure Winchester would jump on any chance to protect themselves from a lawsuit.  This being a common debate, it would be in there best interests to make a warning if .308 could be dangerous in 7.62 rifles.  After researching even more, I am finding a lot of information supporting that .308 is safe in 7.62 rifles; I am still looking for a source that my brother came across, which has incredible amounts of data, but I can't find it.

Don't say it's safe either.

It does mention the dangers of .223/5.56 interchange, I assume they would do the same for .308/7.62 interchange.

From another forum:

You missed the point: The U.S. Government is not beholding to SAAMI standards, and can pressure test and can use whatever pressure spec terminology it wants. It calls it psi, but it was obtained using the copper crusher method. If you have ever shot 7.62x51 and .308 Win side-by-side, you would realize that there is NOT a 12,000psi pressure difference between them. Also, common sense would tell you that since the .30-06's pressure specs is 50,000 CUP and 60,000psi, there is simply NO WAY that the 7.62x51 nearly duplicates the military's .30-06 ballistics while operating at nearly 17% less pressure. In summary, your assumption that the government used piezo-electric transducers to obtain the pressure specs for the 7.62x51 simply because the government lists the pressure as psi (instead of CUP) is in error.

Scott E White, while TM 43-001-27 does lists the pressure in PSI, I believe it was taken with the old copper crusher method. This was normal when it was the only method available, PSI or CUP were used interchangeably, then came the transducers and SAAMI changed nomenclature to PSI vs CUP. The US Army does have its own standards, that's why they can list whatever they want.

See the NATO standard:

http://en.wikipedia.org/wiki/NATO_EPVAT_testing

Note the SAAMI does not list the 7.62 NATO / 308 Win interchange as unsafe (but they do state that 5.56 may be unsafe in 223 chambers, due to different chamber specs and higher pressure of 5.56):

http://www.saami.org/Unsafe_Combinations.cfm

There is no difference in the external dimensions of the .308 Winchester and the 7.62 NATO rounds. The 7.62 chamber is larger than the 308, easy to see because they have different Go-No Go gages. This is to increase reliability in semi/auto weapons under adverse conditions. For this same reason the 7.62 brass is thicker. The military 7.62 is also has sealed necks and primers, and crimped primers.

The 308 does have a slightly higher pressure, but the main problem that may arise is the different pressure curve due to slower powders that can pound the semi/auto actions too hard.

*later edit*  I have been researching for more then five hours now and am sure that .308 is safe in a 7.62 NATO chambered rifle.  All of substantial and supported evidence supports it.  The only information I can find supporting the opposite is the typical ".308 is 62,000psi and 7.62 is 50,000psi"; through my research I have found this to be incorrect, because 7.62 is actually 50,000cup, not psi.  Since .308 is 52,000cup, there is little difference between the two.  I am sure enough to do it myself, I'll let everyone else decide on their own.