went to the range today and fired 40 rounds of some factory 150 grain fmj 308 thru my norc and the front and noticed i could not even find the paper in the first few rounds at 50 yards. after a short inspection i noticed my front sights came loose and started to shift...infact, it almost shifted half way on the mount to the right. I readjusted it and it easily moved back into the center and shot fine. but after several more rounds it started to shift again, so the accidental knock in the car was not the cause... is this common for this to happen??? i was pissed because i was shooting beautiful 100 yard groups with this rifle prior for about 200 rounds