I have recently built a custom 6MM Remington Rifle with a tight neck chamber,.271, mounted with a 8-32x Nightforce scope using Kelby rings and Davidson bases. I am using 70 gr.Sierra BlitzKing bullets with 50 grains of H4350 powder traveling at 3720 fps. I lapped the rings. I am not certain for sure there is a problem yet, but the rifle was sighted in at 250 yards and as I moved the target out to further yardages, 300, 350, 400 the groups seemed to shift to the left there was some wind and gusts when I did this. I want to confirm this but could it be anything else besides the wind?