OK take me through the firing sequence. Are the shots stringing out in straight line or somewhat straight or is the group becoming a pattern and shooting everywhere?
I have you checked the bore for fouling. If it is a new barrel you could have some bullet jacket build up somewhere that is cutting a groove in bullet jackets coming down the barrel later. If you have access to a bore scope give it a looksee.
You can get Sweets bore cleaner or you can make Humpy's White and do the same thing.
Go to Ace Tru-Value hardware and get a quart or a gallon of the Janitor's Strength 10% Ammonia. Says it right on the bottle. If you get a quart add 4 ounces of Ivory Dish Detergent. Apply it to bore with wet patch on a plastic jag and place the muzzle on the floor on a paper towel folded square and let the excess flow out. If you have copper build up paper towel will turn purple.
Repeat the above and let it sit ten minutes and check it again. If it is purple repeat again and again till the purple stops. Dry bore sell and shoot it again.
I have a 22-250 barrel a guy left here that was shot out. I looked at it and saw it was fouled badly. I laid the Humpy's White to it and soaked it for like two hours and get clean,put it on a 03A3 action and first group on paper was under an inch at 100.
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