Are you shooting off a good bench, solid and non moving? or just plinking off a picnic table. shooting off sand bags? where do you place the bags way out at the end or under the action, do you use a butt bag. All of these concerns make a big difference. closing a .9 group down to a .5 group is often just shooting technique. You say you have a lot of experience, and i do not doubt you. But often a good technique is something that you need tostart over with to learn how to do it right. Work at trigger control, breath control and rifle control. done right, that crosshair should just hang over the bull. How powerful of a scope are you usiing to bench test the rifle, sometimes more than a 9 x scope is needed to get a rifle to shoot better, (actually it is shooting the same, it is just aimed better) just some ideas,
another idea before you spend all the money on accurizeing that rifle, ask your self what are you going to use it for? A reliable .9 MOA rifle is just perfect for a deer rifle and most larger varmints.
Before you shoot the rifle again, take it all apart, and reassemble it, making sure all parts are sitting in tight, clean, and not under tension, make sure you tighten the scope mount to the same torque and do it evenly so as to not distort the action, make sure the scope rings are aligned parrallel, so that there is no tension on the scope tube, make sure they are no burrs or flashing bits lieing under the action or the barrel. when you tighten everything up, gradually tighten up all the screw making sure you draw each screw up just as tight and just as fast as the others. Set the gun on the sand bags and try it with the bags under the forearm, half way out, and under the action, use a squeeze bag under the butt of the stock that guves you your fine aiming. practice getting your cheek in the same place every time, I trained my son to do that buy putting a piece of tape on the stock, he would place his cheek down and then slide it forward till his cheek just touched the tape. That gave him a rebeatable mark for him to hit. and the tape did not hurt his cheek during shooting.
