This is not an uncommon problem with SOME Black Diamonds and SOME Encores. If you have tried several different loads and bullets call Thompson. According to a gun shop I frequent Thompson is replacing SOME barrels in both models for just that reason. My fathers Black Diamond shoots 4 inch groups at 50 yards with a 240gr Thompson sabbot/bullet and 100Gr Pyrodex pellets. Thats not too good I can shoot 3 inch groups at 100 yards with the same load, With a $150 Buck Country 50 cal. Give them a call what can it hurt.