I use the Knight Disc Extreme .50 with 150 grs Pyro. I have found after alot of rounds (and cleaning). that it is a picky with bullets. I have had the best luck with Thompson Center XTP's (a hornaday bullet). In target shooting I was getting 2.5" groups at 100 yds. In the field I dropped a buck at 175 with a shot through the heart. My advice is to keep shooting till you find what works for you gun. But give the XTP's a try there are also inexpensive.