i just bougt a black diamond .50 cal last month and i shot every combination and it wouldnt group at all . the shots were all over the place . every shot was further to the right until my sight was adjusted all the way to the left and it still wasnt enough .so thompson told me my barrel had some tension in it and wasnt straightend right at the factory , as the barrel heated up it pulled the shots off . i sent it back and i got a new one and the new one groups real nice , i even tried it at 200 yds and it shot very well . i found the 777 powder (140 gr) and the hornady 240 xtp bullet , and musket cap worked the best for me , i shot a 1-1/2" group at 100 yds with this combination .send it back and maybe you will get a good one .and one more thing ,i adjusted the trigger before i shot it and lapped the barrel .