When I got my scope the store sold me some used Leupold bases and rings for $20. I can't complain too much because they seemed to be in really good shape. These are the type where the ring base goes into the slot on the front base and you turn it to lock the ring into place. I've never done this myself and I was wondering if there is some sort of tool that makes sure the ring is alligned perfectly perpendicular to the barrel? I lined it up as good as I could with my eye, then I set the scope in the rings and used the crosshairs to line up with the end of the barrel on the lowest setting. I didn't tighten the back ring and adjusted the front ring with the scope centered and then tightened the back rings. Is this OK or do I need to have it done somewhere that has the equipment?