This season a 300 grain XTP mag in front of 100 gr. Pyrodex R/S.
I've found it's more important to place the bullet accurately and that's what this rifle likes best.
I've used several weights and brands over the years and I've found about any good quality bullet placed in the right spot will drop one quickly. But the best bullet made placed in the wrong spot leaves a wounded deer running off.
(Disclaimer - The one exception to my rule was the buck a buddy shot under and took off two legs with a Barnes Expander MZ, took another shot to finish it, but it didn't go anywhere [&:])