Years ago I had a Remington semi-auto .22 that would do the same thing. You could zero the iron sights dead on at 50 yards, get it out the next day and and it would shoot the same 1.5" group 6 inches in another direction. One day it would go right, the next it might go left, up, or down. Put a scope on it and did the same thing. Mine didn' t have anything to do with weather either. I finally sold it for $50 at a gun show. My dad had the exact same rifle, only 10 years older. His will hit dead on the bullseye everytime. Go figure.