Anytime you can draw a straight line/connect the dots on a group, that is the shooter and not the rig. The rig would have put them in the same hole, while the shooter was unable due to various reasons.
Vertical stringing is most likely rear bag/stock placement irregularity and/or/in combination with cheek weld pressure. Simply speaking, push gun down in back differently between shots and the barrel is moved up or down too.
Horizontal stringing is mainly due to inconsistent placement of the stock "in the pocket" and the consistency of muscle use, and the degree of inconsistent orientation of shoulders square to target
I am slightly relieved to see stringing, because that shows I wasn't in my mojo that session. If the rounds are all over the show, then that's the rig, and there is a-lot to consider with that investigation.