You have
got to be kidding with this part of your post!
You thinking that your 44 mag loads are going to disintegrate the Rossi 92 action that is also chambered in 454 Casull?
That seems strange since the .454 Casull is rated to over 60 000 cup, while the 44 magnum is rated to a much more moderate 40 000 cup.
Do some poking around on the internet.
Guys are loading their 20" .454 model 92's to over 2000 fps with 300 gr bullets and generating around 3000 ft/lbs of energy...
Guys have tested the 20" Model 92 rifles with hundreds of rounds of full power .454 handloads and not found fault with the
strength of the rifle...
I could go on and on...
The Rossi is not the fanciest thing on the block, and fit and finish are good, but not great, the sights are often considered in need of upgrading, and the actions can sometimes be a bit gritty, but any (sane) .44 magnum load disintigrating them is just silliness...
Rant off...
To speak to the OP's question, for bear defence, I would get some good hard cast 300 gr GCFP bullets and load them as fast as I could.