On your video, on your 40x with dead body mass, vs not, doesn't that signify that there's some sort of flex in your stock causing inconsistencies when loading your body in it?
I mean it could also be be the recoil pulse, but I figured if you have consistent recoil pulse, then it should be consistently shot. If you took that rifle and just locked it into a lead sled, removing all input, does it also shoot poorly?