Dusted off my old Mk1 Rapid 7 & went out to zero a new scope. H&N pellets. Done in a few shots, 2 mags showing tight one hole groups, perfect, next mag I thought I saw a streak from the pellet & it hit slightly to the left, had a bigger group & saw the spiraling streak a few times. I left the scope settings thinking new scope so is it head position critical ? Next mag the pellets dropped in a neat line & still to the left, starting to sound like out of air as you now would guess. I've done this quite a few times on other rifles but never going off center before dropping. Repeating again next week to see if it happens again. Is it wierd or common to go off center when the air runs low ?