I've seen patterns like that when a guy lays the gun over the bags on the first shot but allows the gun/barrel to slip backwards and make contact with the bags on successive shots, moving those shots up. Even a free floated barrel can make contact with the stock if the shooter has a tendency to really lay into the gun as he gets a little warmed up. Another thing I've seen is the target itself changing position as it gets hit by bullets. Also, when I can't figure out why my gun won't shoot right, I always do a primer test by loading up about 7 shots of every type of primer I can get my hands on. One other thing to try is experimenting with a contact point at the tip of the stock so the stock and barrel make about 10 lbs of contact pressure. That's more or less how many Ruger 77's come because according to Ruger, they shoot better that way. Could have something to do with that unconventional angled action screw.