Interesting......as far as the "loose nut", I have learned to hold the rear bag to keep things stable,but every once in a while I do catch the rifle has eased back and is resting farther up the stock than I like. The next 2 groups fired (different loads) were round. So the rifle position may well have been the problem. I am usually in a bit of a hurry to get started shooting, and the vertical group was the first one. As far as retreshing the crown, what is your take on the different angles of cutters available ?I'm not sure how your rifle is put together. About 99.218% of my accuracy work has been on Remington, Winchester and Ruger rifles. Some of those have a magazine box that fits in the stock mortise and is only held in by the trigger guard and 'bottom metal' that the tang screws go through. MANY times the mag box is taller than the natural space between action and bottom metal. that puts a 'bow' in both parts. I like a sixteenth clearance to make sure the action sits down in the bedding straight, solid and square.
Now that we covered the rifle and scope maybe we should take a look at the 'loose nut behind the trigger'.
If the toe of the stock is resting on the bench top, it causes vertical stringing. If the barrel is resting on the front rest, it causes vertical flinging. If you drape your hand over the scope to push the rifle down (instead of squeezing the rear bag which controls elevation), vertical displacements can happen.
Round groups are almost always a sign of a healthy rifle. Big and round makes the barrel the suspect. Clean it and re-fresh the crown (88% cure rate) before scrapping the barrel.