For sh*ts and giggles, try firing a couple shots by letting the barrel cool down completely between shots. If the vertical grouping is dispelled then the whole issue centers around the barrel walking as it heats up. Also if the first two shots one right after the other puts the bullets into a satisfactory "group" I would probably hunt with it as-is. Those third, fourth, fifth shots are Hail Mary shots 98% of the time anyway.
That. It ain’t a target rifle
