Running .308 rounds in a 7.62x51 NATO chamber

[HALODIN]

Hello,

I came across this article whilst trying to work out whether my LDT-M14 is chambered for .308 or 7.62x51 and I was curious what others thought.

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

I was told you never put a .308 round in a 7.62x51 NATO chambered rifle because of the pressure, but the above article suggests the pressure is comparable, it was just measured using different standards, hence the difference values. It hints the real issue is the headspace.

It was proofed in Germany (CPI) AFAIK and so we honor their proof marks in the UK, but what pressure do they proof to? Secondly, if the proof pressure exceeds 62,000 PSI and I have the headspace changed for .308, does that mean I can shoot commercial .308 through it?

Does anyone have any expertise on this area?

Cheers,

Craig.

[Gaz]

No expertise, but I thought the NATO-vs-SAAMI argument was about 5.56mm and .223", not 7.62 and 308?

Certainly had no problems treating 7.62 and 308 as interchangeable in any of the rifles I've shot.

[Mikaveli]

What I've been led to believe is that 7.62 is usually fine in a commercial .308 rifle, but it's not always the case the other way round:

"Nobody makes 7.62MM ammo that isn't to the .308 headspace dimension spec. So 7.62MM ammo fits nicely into .308 chambers, as a rule."

"But in some 7.62mm rifles, the chambers are long (to the 7.62mm military spec). Thus, using commercial ammo in such a rifle is not a good idea; you need stronger brass. Use military ammo or possibly the best commercial only at your own risk."

"If you have a chamber with headspace much in excess of 1.636 (say, 1.638, SAAMI field reject), you must use only NATO Mil Spec Ammo (always marked 7.62mm & with a cross enclosed by a circle)"

Source (reworded slightly): http://www.fulton-armory.com/%5Cfaqs%5C ... %5C308.htm

[HALODIN]

Thanks for the reply, I didn't realise this was a long running debate albeit in a smaller caliber... Your experience echos what I'm hearing, but airing on the side of caution, I'd like to know what pressure the CPI proof both 7.62x51 NATO and .308 to if anyone knows. There's also the issue of headspace between the 2 calibers. I've read some horror stories where headspace has been blamed and as a relatively newcomer to the sport, I just want to be safe.

[Sim G]

I had a Tikka, the old proper one's, in .308. I would run surplus through it as it was plenty full then. 7.62 was never as accurate as .308, likewise, 7.62 brass would extract, but never eject. 308 brass would sail through the air....

Both were safe IMO, go figure...

[HALODIN]

Yes this is what I was led to believe as well. I've fired an e-mail to the manufacturers because my M14 is labelled as both 7.62 on the rifle and .308 in the paper work and well they're not strictly interchangeable for the reasons we both linked to. I'm curious what other people think, experience counts for a lot and I don't have a lot (yet!)

Are you shooting tonight? Is Jamie coming as well?

What I've been led to believe is that 7.62 is usually fine in a commercial .308 rifle, but it's not always the case the other way round:

[Mikaveli]

Thanks for the reply, I didn't realise this was a long running debate albeit in a smaller caliber... Your experience echos what I'm hearing, but airing on the side of caution, I'd like to know what pressure the CPI proof both 7.62x51 NATO and .308 to if anyone knows. There's also the issue of headspace between the 2 calibers. I've read some horror stories where headspace has been blamed and as a relatively newcomer to the sport, I just want to be safe.

The CIP lists .308 as 7.62 x 51

Saami doesn't list .308 in 7.62 x 51 in its record of unsafe combos:

http://www.saami.org/specifications_and ... ations.pdf

[HALODIN]

My Imbel FAL is similar, it loves Hornady .308, but 7.62x51 GGG rounds stick when the chamber gets hot, but Hornady match .308 ammo runs all day long no problem extracting at all, but it is chambered .308.

It's accuracy that's driving these questions really. I put a scope on it for the first time this week and it wasn't as accurate as I recalled when it was in the old wooden stock over iron sights. Now I know I was slapdash bedding it in, which I'll fix and I also know that a roll pin that was cited as "optional" probably isn't, but even still I want it to perform as well as it can, so .308 match ammo or handloads are the way forward. A 5 shot group was cited at 1.9cm, which I'm nowhere near ATM. Much closer to 3 inches which is 400% worse. The barrel is a 1:10 (barrel length 55.9 cm) and I know the GGG is only 146.5 grain where I should be looking at 155 but probably closer to 175 for that twist. So I'm led to believe anyway...

I had a Tikka, the old proper one's, in .308. I would run surplus through it as it was plenty full then. 7.62 was never as accurate as .308, likewise, 7.62 brass would extract, but never eject. 308 brass would sail through the air....

Both were safe IMO, go figure...

[HALODIN]

Quite right it's CIP not CPI...

It looks more like an omission to me. I've trawled the CIP website as well and I can't see the info I'm after.

http://www.cip-bobp.org

The CIP lists .308 as 7.62 x 51

Saami doesn't list .308 in 7.62 x 51 in its record of unsafe combos:

http://www.saami.org/specifications_and ... ations.pdf

[lapua338]

The http://www.accurateshooter.com website is quite useful.

http://www.accurateshooter.com/cartridge-guides/308win

Scroll down page to "308 Win vs. 7.62×51–The Straight Scoop"