That's my 454 Casull Handi Rifle. I have topped 2,100 fps with H110 and the Hornady 250 gr FTX. It is reliably accurate out to 150 yards. At 200 yards, it gets a little stringy.
The SB2 Handi rifle is rated comfortably up through 460 and 500 S&W, so the Casull is perfectly safe in it. How Rossi allegedly gets a 92 based lever gun up to Casull levels has never been adequately explained.
The trick is finding an H&R Buffalo Classic Carbine in 45LC, no longer made. Most of them will chamber 454 brass already! Three or four turns with a rifle reamer (very important to get the gentle taper into the leade rather than the sharp forcing cone of a revolver throat) is all most people have needed to convert to 454 Casull. As a side benefit, they all seem to shoot 45LC much better after reaming.
This thread at GBO willl give you the location of some BCCs already converted to 454 or in the original for sale and access to the Forum reamer should you so desire to join up. I love that little rifle. It is fun, a thing of beauty, and very effective on hog and bear.