I have been trying to get a solid zero out of my MP-15. The zero seems to change every outing. I've gone through a red dot, and 4 scopes. I seem to get dialed in at 50' or 25 yds and then at 100 yds I can't hit a 24" X 40" target. I took it to the 50' range and dialed it in today. But the holes in the target were not round. They looked like the round hit sideways.Any thoughts? For the record I have an MP15/22 and an AR chambered in 9mm. I also shot expert back when at Pendleton and 29 Palms with an M16-A2.