I tried adding weight to my bench rest rifle by having a brass spacer made that fit between the stock and the rubber recoil pad on a Ruger/Kidd build. The added weight, don't remember how much we added, balanced the rifle directly under the chamber. Group sizes blew up, gun would not group shots at all. Removed the weight and it went back to shooting one hole. Never did figure out why it acted so crazy, I all ways thought it may have had an unwanted affect on the barrel harmonics or the balance point shift was causing the rifle to lift or bounch off the front rest.