Can't see it being pellets. If it was pellets, it would fail to group ALL the time. It's had AA, Daystate, but primarily JSB's through it. All 4.52. Even gone to the extreme of sizing them as well. Same results. I reckon it's the barrel that is cleaning fussy rather than pellet fussy. Even so, you would think that the groups would only open up slightly if it was barrel cleaning. Then, why tighten back up again? And what could cause the odd pellet to go inches astray? On the FT course, I've known it miss a faceplate completely at fairly close ranges.