The .45 Colt CAN be loaded hot, and with the right bullet CAN be as effective on bear as an equivalent hot & heavy .44 Magnum load.
Most factory offerings are not in this category, though.
You need either a hardcast solid lead bullet (preferably) or a stoutly constructed JHP that won't break up before penetrating deeply, to achieve best results.
That does not mean any of the mild "cowboy" competition loads, and it doesn't mean most of the relatively soft and/or thin-jacketed JHPs on the market.
Once you get up to the truly effective .45 Colt loads, you're also looking at increased recoil.
I've fired some of the heavy CorBon .45 Colt "magnums" through my Rossi, that'll never happen again.
The ML design is simply poorly configured in the wrist area to control heavy recoil. Without a pistolgrip, like a conventional revolver, the gun tries to slide straight back in the hand. I banged the inside front of the lever bow against my second finger right noticeably.
Recovery time between shots is slow to begin with, since you have to bring the gun down well off the eyeline to cycle the action & return it up to that eyeline to re-acquire your sight picture, and the recoil recovery time adds to that.
None of the defficiencies of the whole package compensate for any slight gain in velocities through that longer 12-inch barrel, for me.
And- DO NOT try to fire one of these with a stiff load by placing it against your cheek while aiming through the sights!
Denis