I think you should be fine with 100 grains of pyrodex, but you might consider the 338 grain platinums. Either will probably do ok, although I use the 405 grain aerotip.
that said, 90 grains would be plenty also if they group well.
And you may want to try the new Hornady 350 gr FPB bullet. Did well on an elk for me. I think they will hold together better than powerbelts. JMO.
txhunter58
venor, ergo sum (I hunt, therefore I am)