375,

That's basically the jist of the 450#2. My No.1 drives a 500gr bullet at 2150 fps, and does so at a much lower chamber pressure than the .458, as Bramble pointed out. It's a very doable conversion. I had SSK re-chamber a factory .458 Win Mag, and they did a great job of it. I've since re-barrelled this gun(again in 450#2) because I just didn't care for the poor muzzle heavy balance of the factory gun.

Jeff