Iirc the Remington 45/70 boxes has it right on the box, safe to shoot in anything chambered for 45/70, at least some of them do.
This would make them fairly anemic in modern guns, by my way of thinking.
I know ww guns in Anchorage modifies marlins and calls them 457 mag, I do not know what all is entailed. I do know they advertise that you can also shoot 45/70 ammo in them.
I do not know how many of these they have sold, but there has been at least a few of them.
I will say this, I do not consider it feasible to claim a slow moving 405 grain bullet would do the same as a faster one, I would think even 300 fps would make a difference in the shock, even penetration when hitting heavy bone.
Will the trap door loads kill anything in this country, you bet, BUT you will not see me carrying them in grizzly country.
I need to look it up, but I am not 100% sure trap door loads are even legal for buffalo here.