it doesn't move any if...

it fits well to begin with. Cut it so that the liner fits tight against the inner wall without the edges over-lapping, and put the edges opposite of the cocking slot. The tendancy of the plastic is to open up or un-roll, which holds it tight to the inside. The amount of surface area of the spring, which is lubricated, is minimal compared to the surface area of contact to the inner wall of the piston. I have not seen another shift in any of them so far, and a couple of the rifles have 500 or more shots through them. You should polish the part of the cocking shoe that could potentially come in contact with the plastic through the slot in the piston. I have installed them in two Quests, a Sierra, a B-3 side-lever, two B-3 underlevers, a CFX, and maybe one or two I forgot about. Anytime there is clearance between the spring OD and ID of the piston, I try to fit one. You will not beleive the difference it makes, until you try it!