Pitch the pellets. If they are old they do not age well and don't burn properly. Need new every year OR get loose powder and get a fine tuned load. at any kind of range beyond 10" those powerbelts will do OK with that load. More information on the terminal performance, bullet "grenading" ? no mushroom and just stop on bone ? what range and angle were shots ? which belted bullet, pure lead HP-copper HP, copper aerotip- would help troubleshoot problem. Reflects my experience and opinion, yours may be different. W