The Firing Line Forums - View Single Post - Safe to shoot 7.62x51 in Ruger American .308?

Bart B. · February 8, 2013, 08:28 AM

PawPaw, you're confusing the old MIL SPEC standard of stating cartridge pressure in "psi" units when they acutally used copper units of pressure (cup) systems to measure it. But commercial ammo standards did the same thing for decades so they've both been using technically incorrect terminology. Both cartridges' pressure specs are within a few percent of each other. But most folks have mixed this up over the years; you're not alone. The original specs established for the 7.62 was 50,000 cup and the .308's was 52,000 cup; both originating at Winchester with a bit of help from one or two arsenals.

Take a look at the following:

http://www.saami.org/specifications_...wnload/206.pdf

then scroll down to the pressure information that's listed in both CUP and PSI numbers as well as the sections showing how each is measured. You'll see quite a difference in the numbers for each method. It's also interesting to look at the proof load pressure specs that are higher than normal ammo.

Compare the specs section for pressure in the following:

http://en.wikipedia.org/wiki/.308_Winchester

http://en.wikipedia.org/wiki/7.62%C3%9751mm_NATO

rc, exactly what is the difference in action strength in PSI numbers between the Ruger and M14 for their bursting limits? I'm curious as to your reasoning behind your claim. Winchester 70's have been in the 120,000 psi range and the Remington 7XX ones in the 130,000 psi range for their bursting points. But its the case rupturing limits that determine peak pressure for ammo, not the rifle. The case is the weakest part of the system 'cause it's not totally supported by action metal. I doubt the Ruger would stay intact after several hundred (thousand?) rounds of proof loads whereas the M14 (and M1, too) did so with some of their match ammo peak pressures at the same or higher levels than proof loads.

February 8, 2013, 08:28 AM	#8
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	PawPaw, you're confusing the old MIL SPEC standard of stating cartridge pressure in "psi" units when they acutally used copper units of pressure (cup) systems to measure it. But commercial ammo standards did the same thing for decades so they've both been using technically incorrect terminology. Both cartridges' pressure specs are within a few percent of each other. But most folks have mixed this up over the years; you're not alone. The original specs established for the 7.62 was 50,000 cup and the .308's was 52,000 cup; both originating at Winchester with a bit of help from one or two arsenals. Take a look at the following: http://www.saami.org/specifications_...wnload/206.pdf then scroll down to the pressure information that's listed in both CUP and PSI numbers as well as the sections showing how each is measured. You'll see quite a difference in the numbers for each method. It's also interesting to look at the proof load pressure specs that are higher than normal ammo. Compare the specs section for pressure in the following: http://en.wikipedia.org/wiki/.308_Winchester http://en.wikipedia.org/wiki/7.62%C3%9751mm_NATO rc, exactly what is the difference in action strength in PSI numbers between the Ruger and M14 for their bursting limits? I'm curious as to your reasoning behind your claim. Winchester 70's have been in the 120,000 psi range and the Remington 7XX ones in the 130,000 psi range for their bursting points. But its the case rupturing limits that determine peak pressure for ammo, not the rifle. The case is the weakest part of the system 'cause it's not totally supported by action metal. I doubt the Ruger would stay intact after several hundred (thousand?) rounds of proof loads whereas the M14 (and M1, too) did so with some of their match ammo peak pressures at the same or higher levels than proof loads. Last edited by Bart B.; February 8, 2013 at 09:53 AM.