If you want a big hole use a 12 ga slug gun. Even with sabots you would be shooting a .50 cal bullet. With a standard rifled slug like brenneke dangerous game slug you would leave a whole the size of a quarter. And some of the newer slug loads are the same as a standard 45-70 load. I mean if you want big and heavy it's hard to beat 70+ caliber and 600 plus grains. Or even 435 grns for a standard sabot slug.

However that is no comparison to a properly constructed bullet at a high velocity. High velocity projectiles do a LOT of damage to tissue, even if the bullet isn't that big. Shoot a varmint with a slug gun, then shoot one with a 22-250. The smaller faster bullet will blow it apart. With the proper bullet any high powered rifle should be very lethal on a bear if you make a good shot. Make a bad shot and you could be using a .50 cal BMG and it might not make a difference.

Paul