I concur with the scope being the problem. The internal mechanisms can get loose over time. I just sent back a Zeiss Conquest for service because something inside came loose after about 1000 rounds of ammo was fired through the rifle it was mounted on.

I seriously doubt a pitted barrel is the problem based on my experience with a model 1891 Mauser thatI left to rust forabout 20years. The bore is severely pitted. However,with this rifle I can put 5 shots into a sub 1" group at 50 yards withits iron sights. At 100 yards it shoots2to 3 inch groups. I'd like to know what I could do with a scope mounted on this rifle, but I'll never find out since I want to keep it original.Yes,a pristine bore is nice, but notalways necessary.