I'd rate it at 90% chance you have a bad scope, loose rings, or both.

I have a Tikka in .243. An accuracy problem like that would be very unlikely to suddenly develop. Since it does not appear that you handload, it's a pretty safe assumption that you didn't damage the chamber or barrel with a bad powder measure or some other charging issue that resulted in over-powered loads.

I'm going to assume that you don't use this rifle for high-volume shooting such that you've run 10,000 rounds through it in the last year? Obviously if you've spent the last couple of years blazing away with hot loads at huge numbers of p-dogs, it's possible that you've shot the barrel out. I find this highly unlikely as no one short of Warren Buffet could afford to do that using factory ammo.

The only other thing I can think of is if the stock has somehow been attached wrong such that it's not free-floating. This is a remote possibility, but worth checking.

Grouse