I have an Ultimate Firearms Inc. "Game Breaker" that I've only shot a few factory .450 Bushmaster rounds from. I haven't reloaded CF ammunition in decades, being a dedicated muzzleloader shooter.
The rifle has a Leupold VX6, 3-18 scope and I chose the 3 shot magazine over the 5. This rifle shoots excellent with outstanding accuracy with factory ammunition.

I loaded up my first box of .450 Bushmaster with Federal 205 primers, 37.9grs LilGun and the Hornady 250gr. FTX bullet. Fortunately I had another shooter help with the setup.

This morning it was cool enough to try my first reloads for the "Game Breaker" and it worked out well. I do have to say, Ken Johnston makes excellent rifles, not just muzzleloaders. http://ultimatefirearms.com/

Range: 150 yards....... 3-shot group