Something like this?
Take .50 BMG lead bullets, turn the nose down, and end up with around 700 grains.
That said, stabilizing that big a bullet out of a short barrel, with the wrong twist maybe a problem. Is it John Ross that knows the .500 backwards and forwards? I think that's it. He isn't too keen on that heavy a bullet, and, keep in mind it works in my .510 Linebaugh, but not in the .500JRH, because of the diameter difference.
To be real, isn't 525 grains enough, out of near any handgun?
Bullet on the right, next to the .500 Nitro Express round is a 525 grain LFN for the .500 Linebaugh Max. Goes 1350 fps out of my gun, and, I loaded about 100, and still have 90 around. When I want to shoot it, I just go out, put my hand on an anvil, and hit it with a baseball bat at about 82 ft-lbs of energy. Same difference.
By the way, the Linebaugh boys swear the 525 at 950 fps kills like the Thor's Hammer.
As for .500 Special brass, I think that is Hamilton Bowen, 1.2" S&W case. the .500JRH is a little longer, but still fits in a standard size gun, 1.4" same as the .475 Linebaugh.