Re: Your thoughts
In general, horizontal stringing is caused by bore bedding and vertical stringing is caused by bolt lugs that are not fully in contact.
Now this is in general as a stock hitting a barrel can do many strange things.
That said, if the rifle shoots well with lower pressure loads but gets fliers when the pressures increase, more then likely its a bolt lug issue. At lower pressures one lug can support the round, as the bolt thrust increases with the increased load, so does the flex in the bolt and generally you will see vertical stringing.
Pull the bolt, and look at the contact areas and see if they are both contacting the receiver. If this is a new rifle this may be difficult to tell for sure but you can generally tell if you have a floating lug.
The cure???? If it is close, lapping it in will do most of the time, if it is floating a significant amount, the only correct fix is to pull the barrel and square up the receiver. It will also require the barrel to be set back slightly to set the headspace back to where it should be.
Check the stock and mounting hardware first. Then look at the bolt lugs to make sure they are making even contact.
If they are all checking out, them check to make sure the receiver screws are not TOO tight. This can flex the receiver in an HS stock and cause fliers as well. A simple stress free skim bedding will cure this if it is the problem.
I have yet to see any HS stock that did not perform better after being skim bedded then before it was bedded. At least accuracy never has decreased after skim bedding.
Just a couple more things to check on.
Other then that, you may have a barrel with a stress in it that rears its head when the barrel warms up!!
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