Yup as above, some 7.62 brass will have reduced case capacity. It's best to measure your case capacity in grains of H20, that way you will know for sure.
As for pressure.
The pressure in the .308 and the 7.62 virtually identical. The 308 runs at 62Kpsi the 7.62 Nato runs at 50K CUP not psi which equates to about 62K psi. The 7.62 was never testing in psi it was tested in CUP and some dumb ass in the US Military exchanged the CUP for PSI in an official document and has cauised mass confusion ever since.
If you look through military ammo specs from before the mid-90's, you find military copper crusher numbers reported as "psi" at the same time a commercial maker would have reported them as "CUP" (I don't know why "CUP" gets caps while "psi" gets lower case, but that's how SAAMI publishes them). The SAAMI conformal piezo spec is 62,000 psi MAP (Maximum Average Pressure). I'll have to check, but I recall SAAMI MAP allows up to 4% deviation from average, so 64,480 psi would be the allowed extreme spread in SAAMI compliant ammo.
The NATO allies use 415 MPa, which the CIP uses for both 7.62 NATO and .308 Winchester. That converts to 60,191 psi, but the CIP measuring system sets the sample point further forward in the case, so it sees a bit of the pressure drop at the bullet base that occurs when the bullet starts moving. That makes them tend to read about 2,000 psi lower than the SAAMI setup does in this pressure range. So the same ammo would measure closer to 62,000 psi in SAAMI equipment.
http://www.ar15.com/media/mediaFiles/348/32231.JPG
Now take the load data from the document above (172gr bullet, 44gr IMR-4895) and compare it to some 308 Win data in your loading manuals. You will see that there is no way that this load of 44gr IMR-4895 can be running at 50K PSI. It is Running at 60K PSI or 50K CUP.
You can also go to Midway and check out their ammo. Note the Federal 7.62 ammo has identical ballistics, fps, fpe as the same load in 308 Win. Only way these two can have the same ballistics is if they are running at the exact same pressure.
http://www.midwayusa.com/product/953...open-tip-match
http://www.midwayusa.com/product/953...oint-boat-tail
http://how-i-did-it.org/762vs308/chamber.html