I am by far no expert when it comes to BP, but I have the same rifle that you have.

I can't vouche for a good grain bullet because I have yet to have the chance to test the ones that I am currently using. I tried to use Powerbelts when I first got the rifle, but I never got good groupings with them. Didn't matter if they were the aerotip or the hollowpoint style.

I am now shooting 200gr. T/C Sockwave and have had great success on the range as far as groups and accuracy. Like I said, my choice was limited at the local stores, so I am going to try the 200gr for now.

I also agree that buying the .45 may not have been the best idea when I bought the rifle, but then again, its still a lot of fun to shoot.