Keep it simple. Nine times out of ten, dancing rounds on paper are optics.

You can check the bases and rings, but you should probably just mount another scope on it. One that you know is good. If that gets your groups back, you know your cross hairs are driffting. Happens a lot. Especially a rifle that rides next to you in the truck. More often then damaged crowning. Not ruling that out, but it's way easier to check the optics first.

My guess would be that it is a problem with the scope also. I just can't see the gun going bad overnight due to any other problem. Damage to a crown won't happen very easily. Heck, when bullets sizzling out of the barrel at 3000 feet or more per second won't do damage to it, I doubt other things will damage it so easily either. Besides, I inherited a rifle from my uncle who cleaned ALL his guns, even bolt actions with the cleaning rod thru the front of the barrel. The crown looks like someone put a file to it, with the many jagged edges he put into the crown with the cleaning rod. The gun shoots as good as any I have, which makes me believe that the crown issue is a bit overrated in regards to accuracy.

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.