Hey bear. Three things come to mind: First is barrel heat. As the mini's barrel heats the shots tend to drop. When working on accuracy I fire slowly check barrel temp with my fingers. If I can't stand to touch the barrel for 30 sec its too hot. I am currently looking for a steel hand guard, with more vent openings. Look at yours, the first 8" has no holes, the material is plastic which is more of an insulator, than a conductor. I believe this will help in cooling.
Second, if your shooting off a sand bag or cheap rest, its important to have the forestock in the same place each shot or the vertical stringing will occur. My Caldwell Rock, has a forestock stop.
Thirdly, your trigger hand weight, and head weight on the stock must be the same, it can really make a diff. as well as your stock butt to shoulder pressure. It must be consistant. This is what I really had to work on when shooting off a rest.
Some misc stuff: When letting your barrel cool, pull the mag with the bolt locked open. Leaving a round in the chamber to heat up will change pressures, as will leaving your ammo in direct sunlight. Keep ammo covered.
Did you bed the top of the stock, under the receiver? It helps, unless you have a Hogue. I didn't mine because its rubber there, but it does fit tight there.
Check bedding, for large voids near recoil lugs, soft spots, cause by exposure to cleaning solvent.
Scope, check rings didn't work loose.
If you reload, the bullet seating may be changing under recoil. It's happened to me.
I assume you know about, 1st Round is manually loaded, where subsequent rounds, are recoil loaded. The first round in a semi auto may be off group somewhat. Hope this helps.