Assuming that the scope mount screws are drilled square, I think the scope base you use is the key to a square mounting. For instance, the Leupold standard scope base has the Az adjustment on the rear ring mount. This would be more difficult to have absolutely square. However, there's nothing wrong with this mount, I use them on several of my rifles with good results. The elevation and windage adjustment on the scope allows you to zero the scope to make up for small problems in the mount. For hunting purposes this works just fine. The Warne single piece base with the insert rings will probably mount more square (assuming the holes are drilled square). I use these mounts on my higher recoil rifles. I don't thing you will note a POI difference in the magnifiaction range with a good quality scope. Once again, this is for hunting rifles not bench rest target shooting.
