Yes, the front ring must be on a straight tube OR a band around the front bell, so the scope pivot won't cause the bell to bump into the rib. The unfortunate answer to claw width is no, they are not all the same. The hope is that many will be the same, or enough the same that a little fitting will make them work. (maybe filing just enough off the sides that they fit down into the slots.) I think the rear mount is most likely to be standard. The front will vary in width, but we hope not depth. In any case knowing where they have to be tight is essential. A good test of tightness is when the rear mount is released and the scope kicks upward just a bit. Yes, it is under tension to a degree, but better than being loose! Making them from scratch can work, and the split rings, while non-original, allow straight tube mounting. Good luck. If you are like many of us, you need a scope sight, so bite the bullet and get er done. Steve
