has anyone experienced problems with this holding zero. It was the.last thing I thought of. Tightened,tryed.different ammo, checked barrel..u name it. The adjustments are off. Ill shoot 3 rounds and make 1/2 moa.adjustment and it will move 3 feet or not move at all. Ill get it.close then take one more shot and its 3 feet off. I have it on a M&P 15 . Can anyone help. Has anyone experienced burris warenty work? Repairs?