.308 Winchester vs. 7.62×51 NATO
Ever wondered about the difference between the .308 Win and the 7.62×51 cartridge?
From 6mmbr.com
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. A commercial .308 Win round can exceed the max rated pressure for the 7.62×51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles that have been designed for 50,000 psi max.
More here.
A UK armourer explains the problems he had using reloaded cases fired from military 7.62×51 rifles in his .308 rifle:
Around this period I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn’t want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn’t fit because they stretched. I was using a Lee Loader in 308 Winchester and didn’t know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle’s chamber! Hmmm…
More here.
Some more more information here:
Hi, welcome to my blog! This blog is dedicated to all things firearms related. I hope you enjoy it.
Hi writing from South Africa I just want to know can a AK47 fire ether a 308 or 303 round?
thanks James
Hi James. There are AK clones, such as the Saiga 308, that fire .308.
I don’t think there have ever been a .303 clone as it is a rimmed cartridge.
Are civilians allowed semi-auto rifles in South Africa?
If you have any ak or variant with 7.62mmx39mm stamped on it then, NO, , the .308, .303, won’t chamber. and may blow the holy hell out of that AK. You COULD, reload the 7.62×39mm bulluts into .303 cases.. They are the sme diameter (.311) .308 bullets are (.30 cal). Also, and i want to say dont try this at home, but i have by accident fired a 7.62×39mm through a smle #1 mark 3 and it just landed about 2 inches high at 50 yards. I wouldnt advise it, but i wonder how much that has been done in afgahnistan.?
62,000 psi vs. 50,000 CUP. Same pressure, different measuring method. Semi-automatic and automatic weapons need more cartridge-to-chamber clearance than bolt actions, hence Winchester could tighten the head space for the .308 WCF. If anything, a max size 7.62×51 cartridge may be hard to chamber in a .308. Anybody attempting reloading ought to do just a bit of reading beforehand, so he wouldn’t have to wonder aloud why his Lee loader won’t produce ammo that can be chambered in another rifle from cases fired in an FAL. Duh! To James: Not unless you chamber it with a hammer. A .303 would enter the 7.62×39 partway, but the bolt wouldn’t be able to close.To Chad: “Accidentally” fire a 7.62×39 in a .303?. Nasty little bugger just snuck into the chamber when you weren’t watching?. You wer lucky you didn’t get a faceful of brass and hot gas.
All you guys for real????
I could use some advice about a different angle on the same question.
I have access to a lot of factory new .308 Win but am short on linked 7.62 for use in a MAG-58.
It occurred to me that I could hand link some of the .308 to fam-fire the MG. The heavier barrel and chamber should easily handle any difference in the pressures but I am not an expert, just a shooter.
Am I setting myself up for failure?
Everything I have read online pertains to .308 vs 7.62 rifles.
Heres an accidental, but instructional event that happened to me. I reload for .308. I shoot two rifles M1A and Savage 10FP, both in “.308″. Recently while shooting the Savage I had brought along some reloads that were “fire-formed” in the M1A. I did not do this on purpose and did not realize it until I went to chamber a round in the Savage. Nope, not happening! Chamber Pressures aside, the Mil-Spec chambers are dimensionally longer, You cant tell the difference looking at the cartridge, and even with a good caliper, its probably not very easy. That “.003″ inch of difference is all it took, in practice, to finally make me a believer that these 2 cartridges, 7.62×51 and .308 are not dimensionally the same.
Jim, very interesting!
Steve,
Thanks, Yes it was interesting because the case necks were trimmed, so it was the movement of the shoulder of the cartridge forward during the “fire-forming” process in the M1A that changed the dimension. Also, I can take a cartridge “fire-formed” in the Savage, neck trim it to proper case length, reload it, and still use it in the M1A. I had read about the .003″ (longer) difference in mil-spec chambers, but this proved that some 7.62×51 designed cartridges really could be “too long”, (.003″ longer) for a commercial .308 chamber. Staring at the two cartridges will not convince you, at least it did not convince me, but this did.
So my rule of thumb is, in general, if you reload:
You can reload cases fired in a .308 commercial chamber for a milspec chamber, but you cant do the opposite. Once its fired in a milspec dimensioned chamber its now what I would call “7.62 dimensioned”.