Another .308 vs 7.62 NATO ammo question.


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mtonetwo
June 30, 2004, 12:07 PM
I have researched the archives here regarding this question but still am somewhat confused.

I just purchased an SA M1A SOCOM and need help with appropriate ammo.

The rifle came with a tag that states headspace is at 1.6315, and states to use GI mil spec or commercially manufactured ammo to GI spec.

So far I haven't seen any commercial ammo (WWB, AF, CCI, etc) at retail stores or on most of the online sites that are listed as 7.62 NATO or 51. All seem to just say .308 Win.

As I understand a headspace of 1.631 to 1.632 is .308 spec and is under the GI milspec maximum anyway.

Why would it be an issue with this rifle whether I am shooting either .308 or 7.62?

Thanks for your help.

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ckyllo
June 30, 2004, 12:44 PM
if you do a search in this board you will find many threads about 7.62 and 308. 308 win is 7.62x51 it is the nato size, so our allies make the same round. with the SA the key part is going to be running good ammo in it. with the right ammo it will shoot better than most of the people behind the trigger are able to do.

molonlabe
June 30, 2004, 01:08 PM
Here is a link with additional details, should confuse you more.
http://www.thegunzone.com/30cal.html
http://www.fulton-armory.com/
go to FAQ/M14 page

Grump
June 30, 2004, 02:16 PM
In my experience, .308 ammo tends to run on the short side of .308 dimensions, which allows a lot of stretch when fired in a minutely longer NATO chamber. NO problem for the first fire.

If you reload and resize to min .308 ammo specs again, you can get case separations in as few as 3 reloadings.

There is a theory that firing NATO ammo in a shorter .308 CHAMBER semiauto (specifically M14 system) can cause a jam-type fit and make the legendary slam-fire possible. Many reports of slam-fires were with GI match ammo, while most were with reloads. Very little data on chamber dimensions before the kB! has ever been published. It remains a subject of much controversy, legend and possible superstition.

The M14-type case separations I've seen leave more brass connected to the casehead than that new plastic/metal combo ammo uses. The gases have always remained contained, and the front halves have always ejected--except for one L1A1 I was shooting with those 4-x reloaded cases.

Master Blaster
June 30, 2004, 02:36 PM
My understanding is that 7.62x51 and .308 ammo have identical dimensions per SAAMI.

The difference is in the allowable variation caused by wear / throat errosion in the rifles chamber.

a military spec will allow the chamber to wear abit more than a commercial spec for .308 will. The possibility of a casehead seperation due to stretching of the case is more likely in a very worn military rifle chamber that still but barely meets military specifications. A very wornout .308 chamber will have the same problem.

Good reloading and rifle maintenence practices should avoid any problems irregardless of which ammo is fired in which rifle, so long as saami pressure specs are followed for the load.

Same holds true for .223 vs 5.56


JMHO YMMV

Mute
June 30, 2004, 02:44 PM
This is America, boy! Use .308s. :evil:

30Cal
July 1, 2004, 12:18 PM
With 1.632" headspace, you can fire either.

HankB
July 1, 2004, 02:56 PM
The M1A is a gasgun designed to work with a certain port pressure. Milspec 7.62 Nato ammo is designed to work at this port pressure. Commercial .308 Win ammo is not - it's loaded so as not to exceed SAAMI chamber pressure, but port pressure is anyone's guess. Using heavy bullets or "high energy" or "light magnum" .308 loads increases the chances of excessively high port pressure. You're probably OK if you use match ammo or light bullet (150 - 168 grain) commercial .308 ammo.

The M1A is supposed to be hard on brass. People more knowledgeable than I recommend no more than FOUR firings before "tossing" the brass, regardless of appearance. And that's with the harder military - not commercial - cases.

mtonetwo
July 1, 2004, 11:14 PM
From what I've read here and over at GunRunner that's the conclusion I came to. Seems it falls right in the middle of both specs.

I wonder if headspace is this closely intended by SA just to avoid these issues? If so one wonders if it is just the trial attorneys causing yet another unnecessary disclaimer by the mfgr.

PieThatCorner
July 2, 2004, 03:59 AM
Of all the individuals in my neck of the woods that own an M1A Match/SOCOM/Scout, including myself (SOCOM), the ammo of choice is PMC .308WIN or Australian Military 7.62x51 ammo... with Federal Match trailing in third place - for cost issues, of course. The PMC, in particular, is what I consider to be the best of both worlds in the Springfield setup: cheap in price & solid in quality.

Grump - good call on bringing up the "slam-fire" issue... indeed, not at all a common occurrence, but the element of such a danger is enough for me to chicken out and stick with the quality ammo. :p

Hey, and while I'm on that little note, I think Springfield just published a warning about the single-feed (manual feed) in some of their 1911's that will cause the "slam-fire" effect; although they don't refer to the actual words as "slam-fire" -

-Jim

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