Judging from the engraving, it may have been a two barrel set when new...shotgun or cape gun as the other set. It may have been regulated with a heavy scope in claw mounts, also. If it doesn't shoot heavier bullets well, that might well be the case. If so, I'd try the 235's at a good clip. I have had my best luck with 4064 powder in my 9,3X74R's.

Nice DR! I wish I owned it, and you had a better one...