Shimming worked. I put a shim around the front bedding screw and headed off to the farm. We had a lot of chores planned, so I didn't get to shoot until late on Sunday.
Great news. The shim got the groups down to 2 inches or roughly thereabouts. That puts into the quit-dicking-around-and-go-hunt range. I'm going to stick with things as they are until after deer season.
I also managed to prove out it was the bullets that caused the problem. I had 10 rounds of the PRVI Partisans. Moose, Angus and I tried a few each. We've got a small pond out beyond one of the 100 yard target frames. All you have to do is fire at where the water meets the muddy far bank and you get a geyser of mud and water-- great for checking function. Sure enough, 4 of the rounds hit nothing discernable. If the pattern stuck, they passed silently into the mud higher up on the bank.
Thanks all for your help.
