Honestly, I don't have a definitive solution and thought someone else more knowledgable would submit. 40 folks have read your post and no one has replied, so I figure I would throw out a suggestion or two.
How is your rest? Any chance it moves, even slightly, with the recoil?
I would suggest to check your bases (did you use blue loctite to mount them with?), but you said you've checked them.
If it wasn't for the fact that it is grouping, another suggestion would be your reaction to the sound of the shot. Some folks react to the sound of the gun going off, just like a recoil flinch. Are you using good hearing protection? Perhaps use plugs and muffs.
Finger placement on the trigger. I have always been taught not to place the trigger in the first crease of your index finger. This can cause you to "curl" your finger around the trigger which when you pull the trigger can cause the gun to pull left or right , depending on which hand you shoot with. Place the index finger on the trigger so that rests on the "pad" between the tip and first crease of the finger. When you squeeze the trigger, pull straight back with continuous pressure.
Control you breathing. Take a few good deep breaths prior to shooting. The more oxygen you can breath in, the more relaxed you will be. Let out a little breath then hold it for your shot.
Are you relaxed when you shoot? I've seen folks walk down range to change or do something with the target, then come back and sit down to shoot. Give yourself time to calm down.
Don't "choke" the rifle when shooting it. Line the gun up on target with a light hold, get into position, then grip it like you normally would and check to see it the gun moves off your aim point. You need to hold it firmly, but not with a death grip.
If anything, maybe some of these suggestions will stir some thoughts and with a little brain-storming we can work it out.
Good Luck!
EVOC ONE
