First off, make sure your scope mounts are set properly then Loctited in place so you won't have any loosening of the screws. Second, did your rifle case get bounced around on your way to the plinking area? Third, what type of scope mounts do you have? Weaver, Leupold, etc..... With your typical weaver mounts, you have to make sure the "feet" grab or fit the channels or rails properly. One could mount them, tighten them and think they are grabbing the channels or rails properly, only to get the scope impacted (even slightly) and the "feet" move in the channels or rails. Same goes for Leupold Dovetail mounts. I always make sure to give the scope a light fist tap after I've sighted them in, then shoot another 5-10 rounds just to make sure it's still on target. Just a tip!!!