You should also take a look at the 458 SOCOM, Wilson Combat is making barrels and such for them. The main difference in the two is the bullet diameter, the a Bushmaster uses pistol caliber 45s while the SOCOM uses rifle caliber. I'm guessing there should be a decent selection of bullets for the Bushmaster due to the 460S&W (i.e. good weight selection and designed for high velocities). Brass is a little cheaper for the SOCOM, it's Starline versus Hornady.

Edit: I meant to look at the 458 in addition to the Bushmaster, the way I wrote it it sounds like I'm pushing one over the other. That said, I would probably go wi the SOCOM, I've come really close to getting one in the past.