I mounted my Leapers 8-32X56 on my 350 and twice sheared the scope stop pin off. The recoil just snapped the screw in two after several shots. Is there a hardened version of that screw to get?
That little screw at the back of the Diana mount is for a european scope mounting system, and never meant to be a stop. Just use a mount with a stop pin and position it over the front of the scope rail. Looks a bit odd, but works.
When I installed the mount initially I drilled a new hole into the rail that would fit the stop screw inside the mount. I believe it was the length of the stop screw that led to the breaking. If you thread the stop pin inside the mount all the way into the rail it is approx. 2/5 into the rail and 3/5 inside the mount. At least the hole I made was and that is almost through to the compression tube the rail is bolted to. At this point you can actually wiggle the screw inside the mount. Try it with a bolt and nut that are the same size to see what I mean. You can probably wiggle it in the threads a little if you look close. I believe this little movement was all it took to shear those pins in two from the hard recoil of the 350. To remedy this I bought a hardened bolt that was over an inch long and cut the head off and made my own stop screw. It threaded very tightly with no wiggling at all. It looks a lot cleaner than hanging the stop screw over the front of the rail. The scarey part is drilling the hole in the rail. These rails do not come off just by removing the screws. Inside they are peened to the rail stays to the compression tube.