The Diana 34 barrel lock-up is pretty positive even with a worn seal. You might double-check for a broken barrel pivot bolt also (highlly unlikelly). Diana has always been praised for their barrel locking system.
Thanks for the suggestions- It's actually a brand-new gun, with about a 1000 shots through it now. I'm not certain about the barrel seal, but I'll need to check it- sometimes it locks tight, other times it has just a small degree of play, but the barrel actually seems to move a degree or two. The accuracy is a little wacky, it will group very tight right to left, but has a tendency to string shots vertically. If I adjust the scope just a few clicks(An RWS combo deal)it will sometimes seem to over-react and send the groups way too far out of line. I'm waiting for a new scope to get a better idea how it's doing. The last scope seemed like the recoil might have gotten to it, although I haven't heard anything loose inside. Everything on the stock and scope is tight. I don't have a chrono to check the fps, so I'm just trying a few different things at this point. Thanks again for the responses-
Sounds like what I was having happen to me . What I think Your feeling is the rear Gun to Stock screw ( Located in front of the trigger guard ....Front screw is loosening up .
I bet if you snug it back up it will be shooting where you first set your sights / scope . If you are going to do any tuning etc don't use any loctight on it yet . But if you are just going to shoot it for a good while use some blue ( I think loctight ) on it and it will stay tight and your vertical adjustment should stay the same .
This is if your scope mount and or scope rings haven't vibrated / jarred loose ?