My #4 (2-groove perfect bore) has been re-chambered with a .300 Win-mag reamer held back to give a 2" chamber. The resulting chamber takes a .350 Rem Mag case necked to hold .312" bullets.
: I did this conversion in early 1990's, then found Ken Waters had done the same thing and called his version the .312 Express.
: The stock magazine feeds 3 rounds perfectly, but will stove-pipe if more are put in - without alteration. The bolt face, of course, wonderful arrangement it is, requires no modification for the .532" rim.
: Ballistics are rather good, driving a 174gr. Hornady or 180gr. Remington at 2,960fps, about identical to the original .300H&H and the newer .300 Winchester Short Mag. Better constructed bullets are needed for the .312 Express.