There's an infographic going around talking about the interchange between .308 Winchester and 7.62x51mm NATO.
The max pressure for 7.62x51mm NATO is not 50,000 psi, it is 50,000 CUP. 50,000 CUP, in this case, is equivalent to 60,000 psi.
Next, every weapon designed for NATO that fires 7.62x51mm NATO gets proofed with a 140% pressure charge. That's 84,000 psi and the gun must not break to be accepted. That's a pretty sizable safety margin.
The 62,000 psi max pressure for SAAMI is intended to the the absolute limit with a 52,000 psi maximum average pressure.
The differences in headspace has resulted in ruptured cases in some rare instances when .308 is fired in a NATO spec chamber.
Another important difference between .308 and NATO is the leade. Mil guns tend to have longer leades and that tends to lower the actual chamber pressure in the gun. This is for reliability when the gun gets really hot.
I guess the good news is with the ban on importing parts kits with intact barrels, most "7.62x51mm" battle rifles you'll encounter are actually going to have .308 chamber dimensions.
Anecdotally, when was the last time you heard of someones battle rifle blowing up where it wasn't sketchy surplus ammo (which should nominally have been NATO spec to begin with) or a gross error on the reloading bench?
If this was actually a real problem there'd be a lot more broken gun stories out there on the internet because every negative thing in the world gets a thread.
Click here to submit $0.00 US for a lifetime subscription
Posts
Comments
I looked at that same infographic today and something struck me as wrong. Appreciate you putting knowledge to my ... well... lack of knowledge.
ReplyDeleteI recalled a Lake City Arsenal release about it from a long time ago. It stuck with me because this is the sort of mayhem you confound your players with in games like Twilight 2000. I checked my old game notes and found what I'd written down, with a "dammit!" because this meant I couldn't use .308 breaking an FAL be a plot device.
DeleteThe only one I heard of was Ishapore Enfields fed a steady diet of commercial .308 can really get boogered up, but they aren't exactly well-made rifles.
ReplyDeleteAlso I must push up my nerd glasses and point out that yes most guns get fed a proof load to test strength, but when my buddy was working on developing the ACR they got sent to the range with 100 proof loads. The request was let them know how many it took to break the gun. It ate all 100, and he was impressed.
So yeah, even if the guns survive a few proof loads and are still shipped to distributes it can't take a daily diet of the hot stuff...not that that's what you're claiming.
They get fed _A_ proof round.
DeleteThe thing is that in decades of these "incompatible" rounds being interchanged we have a handful of split case necks to show for it. I'll say it again, the only time you see a NATO chambered gun on a forum blowed up it's because someone was using surplus ammo, which is supposed to be the "safe" NATO spec ammo _OR_ a mistake made on the reloading bench that would have killed ANY rifle.
I've read a compelling argument to keep the brass segregated because the case volumes are significantly different and that definitely will have an effect on chamber pressure. But it's got nothing to do with factory loaded ammo interchange.