I shoot (free recoil
) and know I'm not introducing any holding errors.
I have had issues like this before with a new build.
I am also one that uses a very light hold on the gun, let it do it's own thing.
I built a 6.5 SAUM that i couldn't get to shoot under 2-3" grps, with anything I tried. One day I desided to just pull the gun into my shoulder real tight and the first group was in the 2's. This might not be your problem but worth a try some guns just like to be hugged.