I've had one defective ring that was missing the relief cut in it so it wouldn't tighten. Other than that, Weaver style bases vary in size, Burris Zee rings are made to fit most all of them, it's far easier to clamp them tighter than it is to spread them to fit larger bases. For bases that are on the small size, I squeeze the clamp in a dremel vise so the ring will just slide on the base, then the screw doesn't have to do all the work just to take up the slack. I use a Chapman gunsmith screwdriver set and the ratchet handle that comes with it on the slotted base clamp screw. If it's too much though, it will break the screw and that's not good.....be sure to lubricate the screw under the head and the threads to minimize the friction on the install, doesn't take much to break a screw, just ask me!!
Hope this helps,
Tim
