I have a Nikon M223 3-12 on an AR. Decent glass, accurate adjustments and BDC. My problem is the BDC moves too easily. Using it for coyote hunting and use a sling. By the time i get to my set the windage will be moved, sometimes elevation too. The seem to move too easily and do not have a zero stop. Got a good buy, but i think i will sell if I cannot figure out something else. Is there anyway to tighten up the turrets? What about aftermarket turrets? What about rigging up some turret caps. An ideas would be appreciated.