Vol,
I would guess that you know what your drilling is chambered for now, but I agree with kuduae that one so marked would more than likely have started out as a 9.3x72R(or one of the other 9.3s based on the 360 case).If this is the case, I would be hesitant to use 9.3x74R ammo.The older 9.3s have pretty variable groove diameters, but the 9.3x74Rs were fairly consistant.If the groove diameter is much below .365(I have found more X72s .362-364" than others)I would check further.If larger, it is still not sure,because a few X72Rs went to .368-375".When Norma stopped making 9.3x72R years ago, but continued X74R, some American gunsmiths rechambered to X74R.This was not a good idea. Another possibility is some 9.3x72R S&S would chamber 9.3x74R with some interference that raised pressures(I have personal experience with this),but this isn't likely unless the drilling is a Sauer.This is worth the time to check.
Mike
