I have a 1/7" AR-A2 with a 20" barrel. I mounted my 2X7 compact scope to the carry handle with a no brand, 20 year old mount that has a thumb wheel for tightening it to the handle. While shooting 20 rounds to zero the scope, the wheel loosens up. Would a lock washer help keep it tight enough? Is there another type mount that would work better? I am loading 75grn Hornady match bullets for 100 and 200 yard targets.