I would never mount a rifle in a vise to sight in. Not only will it likely cause you POI to shift after when fired without the vise (because the rifle cannot naturally recoil in a vise), but if the rifle is in a hard kicking cartridge, it is possible to crack or break your stock because the stock takes 100% of the recoild energy and because if the vise it can't move. I've heard similar things about the Cauldwall Lead Sled shooting rest if the used puts too much weight on the tray. A vise is useful for cleaning and working on a rifle, but for sighting in and benchrest shooting you're far better off with just sandbags, a bipod or a front pedestal rest with a rabbit ear read bag.