Jack,
I had a similar thing happen on my 111 trophy hunter in 30-06. If it's still in the synthetic stock, then it could be the same problem I had. I had to do a bedding job around the recoil lug area to get it resolved. It would do great for 3-5 rounds at about 1 MOA @ 100, but then would start throwing them high, left, & right. This is my hunting, brush, beat it up rifle, so I wasn't going to put a laminate stock on it, but that may be the best option to try. I put 2 Laminates on other guns and they seem to improve things quite a bit.
Just a thought,
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