308 vs 7.62

[oozlefinch]

I have a Mannlicher-Schoenauer action built in 1907 by Steyr, on which someone has built up a .308 Win sporter. The MS '03/14 is my all-time favorite military surplus rifle, so when I saw the sporter I bought it without much thought, and had put several dozen commercial loadings through it before I thought to compare chamber pressures. The action is very like the Commission '88 action and, while it may be stronger due to better steels, twenty years on, the design is the same. Frank de Haas, in his "Bolt Action Rifles" recommends against just this conversion. I would like to know who did it. The new Schoenauer magazine spool is purpose-built for the cartridge and is marked ".308". I can't imagine anyone tooling up for this thing without a large contract, military or otherwise. The barrel is marked ".308". It is two-groove, 1 in 10" and is probably a Stevens '03A3 replacement. I only use 7.62 NATO or .22 Accelerator in it now. It is more accurate than I.

[John Sukey (Deceased)]

I would agree about sticking to milsurp or handloading at the lower MV and light bullets instead of trying for the high end.
However, NO government issues rifles to its people that blow up! Bad for morale.
I have a 2A and a 2A1 and only shoot milsurp through them.

[303carbine]

I reloaded for my 2a1 and used the starting loads for 308. Nice and accurate and easy on the rifle.

[ganderite]

I have fired thousands of rounds of ammo through pressure barrels (both SAAMI and NATO spec barrels). I used to do that for a living.

Since then I have worked with an ammo company making sniper ammo for military and the police. This ammo has to be submitted to a gov't lab for pressure testing before it is licensed for sale. prior to that submission, we do a lot of our own pressure testing as part of our load development.

NATO and SAAMI specs are written using different measuring systems and test procedures - this is why the pressure limits of the tow appear to be different. The fact is that the limits are about teh same.

Both commercial and NATO develop about 54,000 to 58,000 psi. it varys from lot to lot. i have seen lots of both commercial and NAOo average 60,000 psi. Both were within spec.

The NATO ammo was causing problems. That is why I submitted it for a re-test to two different authorities. Both came back with similar results. "In spec, but just barely."

The Hornady Light magnums stuffs about 65 grains of very slow ball powder in a 308 case. I have pressure tested that ammo too, and if anyhting, it was slightly milder than other ammo.

I have two Ishies. One has fired about 1000 rounds of Canadian NATO ball. No sign of a problem. have not checked headspace, but will.

Other Ishy is almsot unused.

The reports are serious and should not be ignored. I am at a loss to understand the results and suggestion that commercial ammo is the problem.

Two theories come to mind. First, is it possible the Indian 7.62 ammo is lower presure? I have never tested it.

Is it possible that the heavier case of the NAtO round puts less bolt thrust on the bolt? I have no way to measure bolt thrust.

I could oil a batch of NATO ammo and shoot it in my newer IShy and see if I get any headspace increase. That might suggest the mechanism of the problem.

I have some 88 Commision rifles, but no MS. If action is the same as an 88 I would not shoot factory ammo in it (of any type or flavour). Why beat up a nice old rifle? Load for it and reduce charges a bit. At the top end, 5,000psi only gets you another 50 fps. Same thing happens when you reduce velocity a bit.

[Swagman]

My club requires non magnetic ammo use on their range. I have tried to restrict my Ishapore 2A to mil.surplus ammo but so far haven't found non magnetic milsurp. Even Winchester 7.62 grabs a magnet.
Does anyone know of a 50,000psi non magnetic load?
Swagman

[kent9497]

I have seen this argument in magazines, club newsletters and on several websites.

Being a simple lad I was quite baffled by it all. My understanding was that the US military developed the T65 which subsequently became the 7.62 Nato and was commercially released as .308 Winchester.

Obviously the commercial round was offered in a variety of bullet weights but otherwise...

I understand and accept that the military may have somewhat different standards and requirements than a commercial ammunition supplier:

- military use does not consider reloading
- military specs may well not follow SAAMI specs exactly ~ in the case of .308 Winchester I would expect that the SAAMI spec was based on the military developed loads from which the .308 descended
- military specs may well include larger chambers, smaller brass and more generous headspace than commercial guns and ammunition to allow for dirt and less than perfect ammunition being fed into the gun - the goal is to allow soldiers to shoot successfully in adverse conditions with little regard for reloading brass or benchrest accuracy

Be that as it may the cartridges are for all intents and purposes interchangeable dimensionally and have the same roots.

Being simple and confused I wrote to Remington and Winchester for their comments.

From Remington:

Thank you for contacting Remington Arms. I'm not sure what you are referring to with T65. However, the 7.62x51 and the NATO rounds are the same. The .308 and 7.62 have the same cartridge size and the military chambers are oversized like you mentioned. That said, we do not recommend shooting 7.62 in a sporting .308. The 7.62 ammo is contracted out (in many cases outside of the US) and does not have to follow SAMMI specifications. There is a common problem with excessive pressures with this ammo and that's why the military chambers are oversized. The .308 is not oversized and that's why it's best not to shoot NATO rounds in it.

From Winchester/Olin:

Information I have indicates the T-65 or 7.62Nato is interchangeable with the .308W cartridge. Personally have never had a problem firing 7.62 Nato in a variety of .308W chambered rifles.
Regards,

brian

So if anything it appears that the 7.62 Nato round may operate at higher pressure than .308 Winchester.

[Dimitri]

The NATO round is higher pressure just like its little brother the 5.56x45mm NATO is of higher pressure then the commercial 223Rem. The thing is the "leade" between the cases mouth and the start of the rifling is farther apart to allow the pressure to stop before it builds up in the chamber too much. From what I understand reading many many pages on the web and books about the differences.

Thats why you have chambers like the "Wedley" (not sure of the spelling though) chamber for the 223Rem/5.56mm NATO which is ment to relieve the pressure of NATO ammunition enough to not damage the rifle but at the same time provide a better "Match" chamber that will allow the rifle to be more accurate.

Its WORSE shooting NATO ammo in a commercial chambered firearm then it is to shoot commercial in a NATO chambered firearm from what I understand. Cause the rifle will allow the NATO spec ammunition to build up its pressure but will not relieve it like a NATO chamber would.

But I'm sure that shooting heavier commercial ammunition will hurt the NATO is probably true like was already mentioned. Never mind if its a gas gun like the M1A which cannot shoot alot of powders which do not match its burn rates or improper bullet weights.

Thats why AR-15's, AR-10's, M1A's etc are generally chambered to the NATO spec's and not the commercial ones.

Dimitri