how long are you resting between shots. i was having the same problem with two guns, I shot pyrodex rs and triple 7. shot an 5 shot group the first one almost an bulls, next one high, next little higher, stopped for an minute, loaded up again, that shot almost touching the first and the last shot, was almost touching the second, the barrel was heating up. end up taking both guns to the range with me, shooting one cleaning it. picking up the next gun shooting it. let the barrels cool.