This may not be relevant to your situation but I had the same thing happen to me with a 308, 243, and 22-250 when shooting off shooting sticks. My shots would fly to the right at 200 yards. (I'm a right handed shooter). This didn't occur with my 223's. (I have several - all shot true 100 to 200 yards)
I finally figured out what was causing it. I was holding the rifle too far to the right on my shoulder and I was not square to the target. The recoil, while not severe was enough to cause my body to twist to the right pushing my shots right. After I corrected my shooting position the problem disappeared.
Also, wrapping your thumb around the pistol grip too hard can cause torque and push the shots to the right for a right hand shooter.
I finally figured out what was causing it. I was holding the rifle too far to the right on my shoulder and I was not square to the target. The recoil, while not severe was enough to cause my body to twist to the right pushing my shots right. After I corrected my shooting position the problem disappeared.
Also, wrapping your thumb around the pistol grip too hard can cause torque and push the shots to the right for a right hand shooter.
