Federal XM80CS - cases longer than standard Federal 308 ammo?

[Grizzlypeg]

Just took possession of a case of 500 rounds of Federal xm80cs 7.62 ammunition. When I insert it into a Lyman case headspace gauge, it headspaces out as longer than the permissible length according to the gauge. So I grapped some other Federal ammo and tried two different types of 308 and they both register as between min and max headspace. Why would the XM80 headspace out as over max length? Is it safe to shoot in my M14 that has a tight headspacing of .002 over saami 308 go? I hate to waste the time stripping down my bolt to see if it closes easily on this ammo, but I might have to.

Quoting some info from the net:

"Before we go much further, we want to address the oft-posed question “Are the .308 Winchester and 7.62×51 NATO one and the same?” The simple answer is no. There are differences in chamber specs and maximum pressures. The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62×51 max is 50,000 psi. Also, the headspace is slightly different. The .308 Win “Go Gauge” is 1.630″ vs. 1.635″ for the 7.62×51. The .308′s “No-Go” dimension is 1.634″ vs. 1.6405″ for a 7.62×51 “No Go” gauge.

That said, it is normally fine to shoot quality 7.62×51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical). Clint McKee of Fulton Armory notes: “[N]obody makes 7.62mm (NATO) ammo that isn’t to the .308 ‘headspace’ dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.” You CAN encounter problems going the other way, however.

My comment: Yet it would appear that this xm80 is approx. .005 over the 308 cartridge gauge's maximum length. No idea however to what spec Lyman makes their 308 cartridge headspace gauges to.

Just did a little test. Inserted a 308 go gauge into the Lyman case gauge. It measures between the go and no go limits on the Lyman case gauge. I then dropped a 308 no go gauge into the Lyman case gauge, and it measures right at the no go limit of the case gauge. That seems to verify the Lyman case gauge is pretty accurate. Yet the XM80 ammo measures out beyond the no go limits. What gives? My bolt won't close on a no go.

 

[Ganderite]

The quote about a difference in pressure is incorrect. 308 and 7.62 are both 60,000 psi rounds. The "50,000" for 7.62 refers to the CUP pressure. It is like quoting both mph and kph. Same speed - different numbers.

As for the cases being long - a long headspace may not be an issue. But a too long case is not good.

Take a few rounds, load a mag and chamber them. The bolt probably has enough power to seat the case nicely. measure the rounds after being chambered. The less they change the better.

I use cases that are 5 thou too long in headspace for my Norc 305 which is about +8 headspace.

 

[jonnyc]

Agree. They are the same round....two different names; your mother is also your aunt's sister. Some .308 chambers are cut tight, and as mentioned above, there are manufacturer differences inherent in any 7.62/.308 production. The only real concern is trying to reload max .308 recipes into thicker 7.62x51 cases.

 

[ballistic acorn]

your lyman 308 case gauge is not a 7.62 by headspace gauge as you stated. nor does it mimick the chamber in your gun. the violence of your bolt slamming shut will smash your brass into the chamber. then you pull the trigger and it will happen all over again. nato chambers are obviously sloppier than a 308 chamber. try some out. if m80 is good enough for an m60 its good enough for you. i have fired hundreds and hundreds of rounds of lake city ammo though lots of semi autos: stag 10's, winchester model 100's, norinco m305's, robinson xcr, springfield m1a, i have shot lots and lots of it old and new no pun intended. never any issues except running out.

 

[Terrible Tim]

You absolutely would not be wasting your time stripping the bolt on any M14 type rifle with a tighter headspace 1.632 with any surplus ammo, especially if you are left handed. Its surprising how many won't fit in a clean chamber.

 

[Grizzlypeg]

The ammo shoots fine. I ejected chambered but unfired rounds, and they barely had any mark from the firing pin. The bolt closed fully. I also tested the once chambered rounds in my Lyman case gauge, and there was no difference in shoulder position after chambering.