You will have to take my word on this, but it is absolutely not either of these. At the last session I put 4 shots from my 24" barreled .300 Win Mag (no brake) into one hole into the target right along side the .260. The Accutrigger is adjusted nicely and the pull is nearly the same. Recoil and flinching are non factors also. I was solidly sandbagged and am not a rookie shooter.
The groupings came on 3 successive outings with very favorable wind conditions (calm).
The scope is a 3-9 Ziess Conquest in Talley lightweight mounts freshly mounted, torqued properly, with blue threadlocker, as are the stock screws.
What else could cause horizontal groups?
I am going to change seating depths, primers, powder, etc.
But wondering if someone had this problem with the wedgeless Accustock.