I would pick a big bore double rifle for which I am familiar with, in the first place.

But with the second question, like many a 12 gauge or better a 10 gauge shotgun.

But at a few yards, the shot column would be pretty solid I would think, so a 400 or 480 gr SP projectile would be far more effective and easily penetrate and a shot column not spreading much more?

Either way something handy, that points really well, and has two barrels with lots of effective grunt behind them.

That photo with the growling and snarling monster at 8 feet ...