What would cause a bullet to destabilize suddenly? Can shoot a pretty consistent 4-5 inch group at 850 yards , at 900 yards, flight gets erratic and with 0 consistency. I thought maybe the bullet was going subsonic , but according to my ballistics program that should not happen until around 1300 yards. Shooting 270wsm with 1 in 10 twist, 129 grain bullet with a .463 BC at 2950 fps. I am a little confused.