Sorry about that, I'd never heard it refered to as an 81. Around here it's usually called the BLR(Browning Lever Rifle). Now as to your question.. There were variations of this rifle made in some magnum calibers. The rebarrel would entail a lot of extra work and altering a magazine to feed the straight cases would be a chore,, it could be done. The rifle is deffinitely strong enough although I'd bet the rcoil would be a beast.. Perhaps a bit more weight in the barrel. You may also think about the 450 Marlin as ballistics are similar and ammo would be factory available..