I'd use about 55.0gr. to 60.00 H4895. You might find you don't need any fillers with this powder.

I personally prefer cast bullets in the 400gr. to 460gr. range - Lee, Lyman or RCBS. The Lee and RCBS are gas checked, Lyman plain based. Plain base bullets work fine with a gas check seated upsidedown under them or with a thick card wad, like cut from monopoly board.

That said, I used a 350gr. cast (Lyman RN hard, w/gas check) on a couple descent sized black bears back in the 70's from my first .458 2". The first was a slow, 1,450fps load through both 'lights'- bear waddled 30 yards and piled up dead. The second was making 1,850fps, took the bear between the eyes, looking me in the eyes while hanging onto a big Cotton-Wood tree, prior to him climbing. Bullet exited the back of the skull - hors-de-combat.