Sako 75, in .243, with a factory wood stock, not bedded. 22" barrel, not screw cut. Optilock rings and mounts (2 years old). Meopta 3-12X50 scope. Shooting Hornady Superformance 95gr SSTs.
When initially set up with this combination (about 18 months ago), the rifle shot extremely well indeed (touching holes at 100m, if I was on form).
Last autumn, I started to get a series of unexplainesd misses or really poor shot placement. First inclination was to blame myself. But I was still shooting fine with other rifles. So started to test it periodically.
First 2-3 shots of a session would still group very well, often overlapping holes. However, the POI of these holes shifted unpredictably between sessions, by about 1-2 inches. Initially, I made the mistake of firing one round, adjusting the scope, firing two more to confirm, and going home happy without further testing.
However, after this happened 3-4 times, I got suspicious and started firing longer strings. Again: first 2-3 shots on top of eachother, and then they'd start to wander. No consistent pattern to the wandering: the group just started to dramatically open up, to about 3 inches.
I've checked scope mounts - all tight. Scope itself tracks fine.
I'd be EXTREMELY grateful for suggestions!!