I had a Swedish Mauser military rifle that had way too much space between the receiver at the recoil lug and the issue stock, putting excessive up-pressure on the barrel. I didn't want to glass bed it or permanently alter the stock. I made shims from pieces of refrigerator magnet advertisements. They don't shift around under the receiver, and they're easy to cut with that pair of scissors on your bench that you use for such cutting chores. They could be made even less prone to shift by drilling a hold through them for the guard screw.
