Ok, I shot it.
I used 78 gr bullet and 3 gr Bullseye. That should be ~~ 20kpsi and 950 fps.
The recoil felt about right, but the Rimrock cowboy .311" bullets might be soft for 950 fps.
The 32 Colt Long is an unusual cartridge. It wants a heeled bullet. The case mouth cannot get bigger than .299" when in the chamber.
I just shoved the 0.313" cast bullet in backwards, and the nose acted like a heel, and the bullet snapped into place.