A while back I also faced this with mounting a scope on my Buff. Classic. I have to say I agree with Fred and others - I don't think the small gap is the best setup.
I carried it further, taking a T shaped nut with matching # 8 machine screw from local hardware, and used JB epoxy weld to anchor the floating end onto the barrel. Used the T nut as it gave more surface area to epoxy onto barrel to stand up to recoil. I just purchased a heavy scope for the 45-70 and just didn't like that cantelever floating. Using a weaver # 82 scope rail, first drill from the top side the cantelever end for the # 8 screw. Then from the underside counterdrilled part way with larger size bit to allow the threaded T nut to extend up part way into the rail, to keep more lenght of threads. Also bent the base flange of the T nut to somewhat follow the contour of the barrel where it is epoxied. Of course used release agent on under side of scope rail - furniture wax, -- also on threads of # 8 machine screw, should I want to return to my iron sights. Carefully laid out masking tape on rifle to keep overflow off unwanted area. Used fine sandpaper to remove blueing and degreased area for T lug nut, also same treatment to base of T lug nut itself. Mixed up the epoxy after test fitting and set rail assembly in place with the three rear factory and the new front # 8 all tight.
Maybe sounds a bit drastic, but if you want you can later use a small file and shape the epoxy and use flat black paint to make the new attachment look somewhat "factory". On mine its really not noticable, and now the scope is totally solid, the way I feel it should be. Maybe if someone wants I'll dig out the digital camera and post a pic. Worked for me.
Happy hunting and shooting. --- Bob.
