Is 7.62 and .308 the same or not?

Discussion in 'General Rifle' started by Capt'n Mil Coll, Jan 8, 2017.

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  1. This was my post from some time ago. I did a lot of research to come up with this conclusion. I have condensed and clarified my results. I have also included relevant parts of others posts on this thread and I thank you all.

    This is a discussion about whether 7.62x51 NATO and .308 Winchester have different pressures when fired. Some say .308 has higher pressure. Some say 7.62 NATO has higher pressure. Some say they are the same.

    THE ARGUMENT.
    The entire misconception comes from 7.62 and .308 being tested by two different methods.
    SAAMI testing quotes 62,000 PSI for service pressure of .308 Winchester.
    CUP testing quotes 50,000 CUP which is approx. 58,000 psi for service pressure of 7.62 x 51 NATO.

    Believe me I checked and double checked this information.

    .308 is at 62,000 psi max service pressure. With 83,000 to 89,000 psi for proof pressure.

    NATO EVPAT testing says 7.62 service pressure is at 60,190 psi. With 75,275 as the max proof pressure. This would put 7.62 at a service pressure very close to .308. Close enough not to have to worry one way or the other about higher pressure.

    You can see the actual NATO results here.
    NATO EPVAT testing - Wikipedia, the free encyclopedia

    THE RESULTS.
    So, the bottom line is .308 @ 62,000 PSI, and 7.62x51 NATO @ 60,190 PSI.
    This result is from tests conducted using the same testing.

    Technically, the NATO 7.62x 51 round is lower pressure, but for all intents and purposes, the pressures are approximately the same, and should not cause a problem with any modern firearm that is in good condition.

    PROOF PRESSURE.
    "Proof Pressure is, "The level of pressure at which a component, pipe, tube, hose or other fluid passage will not yield during application of internal pressure. ..."

    It is a pressure at which it has been tested to and found to be safe.
    All European weapons are proof tested and the test pressures stamped on the firearm along with an identifying proof house mark certifying the test.

    HEADSPACE.
    The headspace is slightly different. The .308 Win "Go Gauge" is 1.630" vs. 1.635" for the 7.62x51. The .308's "No-Go" dimension is 1.634" vs. 1.6405" for a 7.62x51 "No Go" gauge. That said, it is normally fine to shoot quality 7.62x51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical). However once fired in a 7.62 chamber, either case may expand large enough to not fit in a .308 Chamber again.

    CASE THICKNESS DIFFERENCE
    Also of note is the case thickness, the 7.62X51 case is much thicker than the commercial .308 brass, this can pose some problems with chambering issues and case head separation depending on the rifle used and reloading techniques.

    A good article on the differences between the two rds. http://www.surplusrifle.com/shooting2006/308vs762nato/index.asp

    As far as I am concerned they are close enough in PSI to be considered the same. Although different chambered rifles may be a problem.

    And I know Wikipedia is not always the best place to find intel. But this does seem to be legit to me.
     
    Last edited: Jan 9, 2017
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  2. SUBMOA

    SUBMOA G&G Evangelist


  3. chesterwin

    chesterwin G&G Evangelist

    It's one of my favorite rifle rounds. Interchanging has never been a worry. Thanks for doing some research!
     
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  4. Big Dog

    Big Dog Retired IT Dinosaur Wrangler Forum Contributor

    My experience says they are NOT the same.
    In SOME weapons, both will chamber, fire and extract fine. In some weapons, this is NOT true. Pressure is not the issue.
    Chamber dimensions are different. The worst problem here is, a once fired 7.62X51 may have expanded (in a military chamber) to the point it won't chamber in my .308Win hunting rifle. Careful resizing may aleviate this.
    Another huge problem is, I cannot use thin-skinned .308Win commercial brass in my CETME rifle, PERIOD. The CETME/HK rifles have a brutal extraction cycle, combined with the fluted chambers, which will rip the thin commercial brass in half. Not a theory, I have had this happen. You end up with a badly designed club.
    So, yeah. Differences. More than just the names.
    Both types of brass are sufficiently available, there is no reason to try to use the "wrong one" in your weapon.
    Now, we could do another thread on the real differences between 5.56X45 and .223Rem.......
     
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  5. Cyrano

    Cyrano Resident Curmudgeon Forum Contributor

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    From what I can tell, the biggest differences between the two are in the thickness of the brass and the headspacing. The civilian .308's No-Go gauge is just slightly coarser than the milspec Go gauge. This in turn means the old saying, "You can shoot .308 Win out of a 7.62 NATO rifle, but not the other way around," while general, is in fact accurate.

    And I agree with Big Dog. The CETME/HK/PTR's roller-locked delayed blowback action and fluted chamber are designed for the battlefield, where no one worries about picking up spent cases to reload and you just want your rifle to work. Because of that, you want to be shooting the milspec 7.62 NATO ammo and not civilian .308 Win. You might be able to shoot .308 out of other types of semi-auto rifles chamber for the 7.62 NATO round, but you would have to test them on a gun-by-gun basis to find out for sure.
     
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  6. YES !......... .308 Winchester & 7.62x51 NATO are the SAME round !........I have a buddy who works at the Lake City Army Ammunition Plant in Independence, and he says the only difference between the Federal ammo & the Military ammo they run threw there is the Head Stamps, besides the obvious bullet weights & powder measures !..............
     
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  7. Txwheels

    Txwheels G&G Evangelist

    I'll just stick with .308 in my .308 rifle.
     
  8. Ten Man

    Ten Man G&G Evangelist

    All my semi-auto "308" rifles are military 7.62x51 chambers, so that is what I feed them.
    All my bolt action "308" rifles get fed .308 ammunition. I keep the fired cases separate, now.

    I used to shoot either ammo out of either rifle, but found out that caused a problem when it came to reloading the brass. Brass shot from a 7.62x51 NATO chamber sometimes will not resize back down to fit in some of the .308 chambered rifles. I found this especially true in the "tight tolerance" high accuracy .308 Remington 700 Police rifle. The brass stretches the shoulder forward during firing a .308 cartridge from an AR10 7.62x51 chamber, and the tightest tolerance reloading die will not size it back down enough for the case to chamber in the Remington 700.

    If it were not for the brass reloading problem, I would not worry about shooting either ammo that will chamber in either size chamber rifle.
     
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  9. PAPA G

    PAPA G G&G Evangelist Forum Contributor

    Back in the Mid-70's I used reloads using .308 Win brass in my M1a Milsurp ammo was difficult to find, and find a gunshop that would order it for me. So I never experienced any sort of difficulty's with it.
     
  10. The fact that a case will fire form to a different size is not the point of this thread. I did cover that in the OP. But the point is that using one or the other round will not "blow up" your rifle.
    And if someone does want to do a thread on .223 vs 5.56 feel free.
     
  11. Big Dog

    Big Dog Retired IT Dinosaur Wrangler Forum Contributor

    I found exactly the same problem with a Remington Model 7 I had a few years back.
     
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  12. Big Dog

    Big Dog Retired IT Dinosaur Wrangler Forum Contributor

    Yeah, that "blow up" thing is a real myth. I have researched over the years, and have never found a verified case of a Spanish M1916 rifle blown up by factory .308Win loads. The few it happened in were hot loaded reloads, sometime insanely hot. Some inexperienced reloaders get hold of bad online data, and don't cross check it.
     
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  13. gandog56

    gandog56 G&G Evangelist Forum Contributor

    Standard answer is sorta kinda the same. Tiny minute differences, most guns will fire either.
     
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  14. shop tom

    shop tom G&G Evangelist Forum Contributor

    Bullshit. The Lake City cases are several grams heavier (I'll weigh some later today and amend this post with that data) than commercial Remington and Winchester .308 cases. Enough to cause dangerous pressure problems for those who do not pay attention to such details.

    Lake City brass NATO brass--177 grains.

    Remington Peters .308 Win. brass--168 grains

    Israeli Arms Nato brass--176 grains.

    Winchester .308 Win. brass--166 grains.
     
    Last edited: Jan 9, 2017
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  15. Big Dog

    Big Dog Retired IT Dinosaur Wrangler Forum Contributor

    I keep my loads moderate, just in case. If you like loading to MAX, then be very sure which case you are using!
    I keep my 7.62X51 handloads for my M1916 at an approximate .30-40 Krag level. Specially marked for that rifle only. It gets nothing else! I have shot factory 7.62 in it, but no sense stressing a century old rifle.
     
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  16. chesterwin

    chesterwin G&G Evangelist

    This pretty much hits the nail on the head. Great explaination. (My opinion but no suggestion made other than using ammo chambered for the firearm.)
     
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  17. chesterwin

    chesterwin G&G Evangelist

    My Savage 112 FV shoots SS109 more accurately than anything I've fed it. It's chambered in .223, not 5.56.

    P.M. Sorry about not starting a separate thread Capt'n. It's relevant info. for both caliber variences in my opinion. With reloading taken out of the equation of course.
     
    Last edited: Jan 9, 2017
  18. gandog56

    gandog56 G&G Evangelist Forum Contributor

    All my statements are null and void if you are loading uberloads.
     
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  19. shop tom

    shop tom G&G Evangelist Forum Contributor

    I do not load uberloads.
     
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  20. shop tom

    shop tom G&G Evangelist Forum Contributor

    Amendment to my above post:

    Lake City brass NATO brass--177 grains.

    Remington Peters .308 Win. brass--168 grains

    Israeli Arms Nato brass--176 grains.

    Winchester .308 Win. brass--166 grains.
     
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