In a tubular fed levergun, there really isn't a pressing need for the 450 Marlin (458x2 with a longer belt) other than giving ammo manufacturers cover for making hot 45-70 equivalent loads that don't blow up weak actions, since no weak actions were chambered in it. Tubular magazine lever guns handle the 45-70 just fine.
Where it shines is in bolt action rifles where it becomes a 458 Win Mag lite. Chambering 45-70 in a bolt action has been done but you really need a bolt action designed for big rimmed cartridges like the Siamese Mauser or the MAS 46. This gets around that and lets you have a 45-70 equivalent in a bolt action.
I hear Browning is chambering the BLR in 450 Marlin now.
