I am lucky enough to own a J. P. Sauer sidelock, sidecocking drilling in 12x12x 9.3x74R. Weight, 7.25 lbs. but very nice to shoot with a good recoil pad. It started life as 9.3x72R Sauer (a propritary bottlenecked cartridge like the 74R). Someone reamed the chamber to 74R and had it re-proofed in Suhl in 1941 in the heat of war! The only problem is the difference in head diameters; the 72R S is .1 mm bigger. If you shoot S&B ammo, you get incipient case head separtion. RWS, Norma, and the new Hornady loads seem to work fine. I only fire the cases once after reloading, however, and loads are kept at factory velocity.
On scope mounts, I dont really like claw mounts on a drilling (although I have them). They really break up the nice, clean shotgun top line, in my opinion. I'm now in the process of making a folding peep sight for the Sauer. You make a treaded steel post to replace the top lever screw and file it square to accept a folding sight blade. Allen screws allow windage adjustment and the elevation is adjusted by filing down a new front post.
While in Reno at the Gunmaker's Guild Show, I saw the new J. P. Smithson scope mounts. Very nice looking but not cheap. Check it out at smithson-gunmaker.com It looked like the cat's meow except he didnt make 7/8 inch rings for my favorite drilling scope, the Lyman Alaskan.
Good Shooting.
