Don't know if there is any more interested in this topic or not but I have been meaning to do more research on it and today the weather was perfect for an extended range trip. I took my Oehler Model 43 Personnel Ballistic Laboratory out and a large variety of ammo to compare. The M43 is a great piece of equipment if you are serious about reloading. Not only does it read velocity but by putting a strain gauge over the chamber it also gives you pressure readings. Before firing any ammunition I first used a micrometer to measure the diameter for the bullet. I used the same M44 for all the testing. This is the caliber I shoot the most and have done a lot of experimenting with it, so I had a lot of different reloads to test. All my loads are straight out of the manual, including the ones using .312 bullets, hornady's manual list loads for .308, .310 and .312, my loads are not max but middle of the road. Just because it worked with my rifle does not mean it will work with yours so work up loads carefully. This was a good excuse to do a lot of shooting. For all except the S&B 180 jsp I fired 5 rounds and averaged the M/V and the chamber pressure, rounding the chamber pressure off. The S&B 180 I only had 3 rounds.
Here are the results:
to get a base line, I first fired, factory and surplus ammo and got the following results.
S&B 180gr jsp .311 bullet diameter m/v 2424 PSI 42000
Privi Partizan 150gr jsp .311 bullet diameter m/v 2830 psi 39500
Russian Surplus 149gr light ball .312 diameter m/v 2813 psi 38000
Reloads
Winchester Brass, Federal 210 primer .308 Hornady 150gr SST IMR 4895 42.3 gr m/v 2415 pressure 36500
Winchester Brass, Federal 210 primer .308 Sierra 175gr IMR 4895 40.1 gr m/v 2290 pressure 39500
Winchester Brass Federal 210 primer .312 Hornady interlock 150gr IMR 4895 43.3gr m/v 2470 pressure 38000
Winchester Brass, Federal 210 primer .312 Hornady interlock 150gr IMR 4895 46.6gr m/v 2690 pressure 40000*
Surplus Russian Ammo, with the bullet replaced
.308 Hornady 150r m/v 2680 pressure 36500
.312 Hornady 150 gr m/v 2805 pressure 38000 *
*These two loads shoot the same in my rifle, both group at about 1.5 inches, I can mix them up and not tell which is which when I shoot them but using the surplus case, powder and primer and just replacing the bullet is a lot cheaper. I have taken several dear with this set up and a lot of hogs. Plus it is fun to work with.