two things that i found....
i have been a 1911 shooter longer than any other gun. you know, two thumbs up high and all that. my glock started to act funny when i installed the extended mag release. i had to take it back out, as i was tripping it without knowing. as far as the groups and the offset, when i thought i had a gun problem i would get one of the RSOs to shoot the gun and almost 100% of the time it was me--grip, dominant eye, and STANCE. i also find that if i'm standing on uneven ground i must compensate. oh yeah, if you are watching the target to see where the shots hit, STOP! front sight--press! have a better day.