7.62 NATO versus 308 Win

[Uncle Jack]

5.62 7.62 NATO versus 308 Win......I have dies marked both ways. What, if any, are the differences in dimensions?

[Eric in NC]

If you mean 7.62 NATO there are some minor differences (you can use 7.62 just fine in 308 guns but not the other way around). For optimal accuracy I would use the 308 dies for a 308 gun and the 7.62 dies for a milsurp.

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.

[Dirk]

The minor difference between the two is in the CHAMBER not the cartridge case. I'm including a dimensioned diagram I found on line. Click Here (http://www.grpc-jax.com/images/308W-762NATO.jpg)

You can use either set of dies for either.

In loaded ammo, it is true that the pressure allowed is higher in .308 Win.

[LaurieH]

In loaded ammo, it is true that the pressure allowed is higher in .308 Win.

Yes, by around 2,000 psi when measured using the same method - not a huge amount in itself. However, the NATO standard for the 7.62mm bullet is 0.3072-.3077", while .308 Win will be at least 0.3080", and most match bullets mike out at around 0.3082-3083", with barrels configured to suit.

The results are that 7.62 ammo usually gives mediocre accuracy in .308 Win rifles, partly because of cheap military bullet quality, but also because they're slightly undersize for the bore and groove dimensions. Do it the other way around - .308W in a true 7.62mm rifle and you can get overly high pressures thanks to the combination of the higher standard plus a tight bullet.

Laurie

[Dirk]

Yep, not much difference at all!

[hunter2]

Article in Shooter mag, Dec. issue on this very subject........