Never use .308 in a rifle cham for 7.62x51mm?

[platoonDaddy]

I always thought they were the same, therefore the question, is this article accurate?

http://how-i-did-it.org/762vs308/chamber.html

[TiroFijo]

I've personally corresponded with several major ammunition manufacturers all over the world, and all basically or textually said that "normal" (not light magnum, etc. loads loaded with slower powders), specially in 150 gr FMJ 308 Win is interchangeable with 7.62x51 NATO. Of course the .mil ammo has a lot more requirementes like flash, bullet pull, sealants, crimps, case weight, etc.

The issue with some 308 loads with slower powders is not chamber pressure but higher than normal gas port pressure that can lead to reliability and durability issues.

I've personally shot or witness firsthand thousands of 7.62 N ammo in sporting rifles, and hundreds of 308 Win loads in real FAL, G3 and M14 military rifles. Perhaps if you fire some brand of 308 Win with thin case walls in a MG with vey long headspace you could have trouble, but not with normal rifles.

The headspace is different from 7.62x51 to 308 Win, but for nearly all makers the round dimensions are the same. Some 7.62 N ammo fit very tight or don't fit in tight 308 Win chambers (that also varies dimensions a lot), but this is very rare. Also NATO has a number of chambers for sniper rifles, machine guns, assault rifles, test barrels etc. etc. So, in that sense, there is no "one" NATO chamber.

[Jack-O]

I can say as an ammo dealer that one of the manufacturers I get product from loads 308 and 762 nato on the same line with the same bullets but just adjusts the powder charge down to meet nato pressure requirements. In many cases adjusting the powder is un needed.

[RiflemanBobcat]

According to that very article, there's basically no difference except the leade of the chamber.

Yet the author goes to all the effort and research to dispel the pressure issues, chamber size differences, et cetera...and then disregards it anyway, preferring to stick with the (just-proven-incorrect) conventional wisdom.

Based on that and Jack-O's info above, my personal take (YMMV etc) is that if you have a 7.62 NATO rifle that is right around GO headspace, or a .308 that's not still short-chambered, you're unlikely to be risking anything by shooting one in the other.


...which reminds me, I have this Ishapore 2A1, the headspace of which I need to confirm.

[platoonDaddy]

From the above posters comments, the article doesn't match their real-world experience. So using both in either weapon is good-to-go?

[gunnut284]

My understanding is that most rifles will shoot both essentially interchangibly but that there are some exceptions. For example, I've heard some of the Spanish military rifles, like the FR-8, were designed for a lighter 7.62x51 round and not intended to handle the .308. Otherwise the issues are with heavier .308 loads in some autoloaders and tolerance variation between manufacturers.

[Jack-O]

From the above posters comments, the article doesn't match their real-world experience. So using both in either weapon is good-to-go?

no. Tirofino summed it up nicely actually. while bolt guns are less of an issue, some older auto loaders dont like the gas port pressures of 308.

as a general rule of thumb dont shoot light magnum or hot handloads in a nato chambered rifle.

[shootist~]

The headspace in a military chamber will normally be a little bigger than in a .308 chamber - assuming both are at near minimums. FN minimum 7.62 (for a FAL) is 1.6315 - SAAMI minimum .308 is 1.6300". US 7.62x51 headspace minimum/maximums are larger that FN's specs (FAL vs M14, anyway).

FYI - there are NATO specs for ammo, but there is no such thing as a common NATO spec for 7.62 chambers. It can vary by country. 7.62 brass is thicker than commercial .308 brass and this probably adds a degree of safety in a chamber that's at the upper limit. (This is not true for .223 brass vs 5.56 brass of course.)

My fired brass from my FN SCAR17 will stretch (at the shoulder) an average of .003" more than brass fired in my .308 bolt gun. (Measured with a Hornady Cartridge Headspace set). The same goes for my FALs (vs the bolt gun) - that I personally headspaced to just over SAAMI .308 minimum spec. Possibly some of this has to do with the semi action versus the bolt, I dunno, but it's about what I expected.

I prefer 7.62x51 surplus or reloads that I have personally worked up in my 7.62 guns. I reload mostly 7.62 brass but I have no problems with using (thinner) .308 brass if needed - *in my rifles*. I don't have a problem with shooting "some" .308 factory ammo in my SCAR17 or FALs (and have done so - especially in the FALs), but I'm careful about what I choose.

Ejection in the FALs with at least one (more-or-less standard pressure) factory .308 165 grain hunting load was very robust compared to surplus 7.62. Same with some warm reloads - so those were set aside for .308 bolt gun use.

The Federal .308 168 grain Gold Metal Match loads I recently ran through the SCAR appear to be just fine based on ejection and inspection & measuring of the fired brass.

Some .308 stuff is also marked as 7.62x51 (Rem 150 gr Core Lock is one). I've shot a box or two in a FAL, but have no recollection of how it performed.