I noticed this weekend while doing load development on my 338 Lapua that my groups all seem to be traveling downward on the target. All of them… After checking out my base, etc.. I noticed these marks on my scope from it moving in the rings. I suspect the reason for the movement is that I have shimmed the rear rings with aluminum beer can. Coke can will not do. Coors original works best. Anyhow.. I have shimmed this scope before in the past and it worked fine. Guess my only option is to tighten down more on the screws? I already have them at 20 inch pounds on the torque wrench. I think its inch pounds. I use the wheeler torque wrench. The other option of taking the shim out wont work really. Long story..but basically I use the Larue QD lever base on two different rifles and taking it out wont allow my 308 any MOA up hardly. After switching my optics over to my LR308 it worked fine with no movement at all. Just the Lapua moved it. Any other ideas to fix this problem?