how hi velocity can you get with a 750 grains bullet in a 500A2??

My .510 JAB's are 500 A-Square's with throats of 0.300" freebore in the 23" barreled BRNO and 0.588" freebore in the 27" barreled Ruger No.1.
The shoulder is 30 degrees instead of 35 degrees with the 500 A2. The standard 500 A2 has .400" freebore.

These differences are trivial, so what I have is two 500 A2's, but I call them 510 JAB, just for fun. 460 Weatherby brass by Norma necked up and fireformed.

Velocities with 750 grain A-Max Hornady bullets in the 23" barrel are 2100 to 2200 fps max.

Velocities in the 27" barrel can be 2200 to 2300 fps max, in my experience.

Nice, reasonable pressure and accurate loads are usually around 2150 fps with 750 grain A-Max, about 1/2 MOA. With a 5 mil holdover, that load will be right on target at 945 yards. You can find it, start at 105 grains of IMR-4350, or 100 grains for prudence sake, and work up with chronograph. 110 grains in the 27" barrel, and 115 grains in the 23" barrel, IIRC, the IMR-4350 charges.

705 grain Harlow target bullets by AAA at 2125 fps will go into about 0.17" for three shots at 100 yards. That is with 110 grains of IMR 4350.

BTW, the 23" barreled rifle gets 2405 fps with 570 grain Barnes XLC's with a compressed load crimped on the cannelure, with RL-15, 110 grains.

The shorter Woodleigh bullets would avoid the compression and/or allow higher powder charges.

My rifles have 1 in 10" twists, instead of the usual 50 BMG twist of 1 in 15". The slower 500 A2 needs a faster twist barrel than the 50 BMG, using the same bullets, IMHO.