What I like about the Burris plastic inserts is that they solved a problem for me. I have a fully rifled barrel shotgun, scope base with Leupold scope & rings. If I optically center the scope and bore sight it, it's pretty far off two ways. I don't like that. I swapped the Leupold rings with the exact same results. That told me Leupold make some consistent rings, but my scope base had to be off. The rear of this base is .005" off to one side and the front of this base is .020 too high. Needless to say a base that is off in both directions is not so good when you are trying to dial in a slug gun for deer hunting at 150 yards. It is nice to have a shop with measuring tools that gives you data to support your effort in making corrections. When I placed the +/- 5 in the back for left and right, and the +/- 20 in the front for up and down. My bore sighter and cross hairs were nearly perfect with the scope on optical zero. I am confident now during the next range visit I will be able to dial in this deer gun. Prior to the measures and use of the Burris brand, I wasted about $60 in ammo chasing my tail.