Have you measured cases before and after, have you measured the chamber depth? try grease on bolt baffel slide rails in the action. Are there any marks on the case after extraction? Blown primers seem to be a concern on a new rifle, unless the brass was weak and charge high, how far off the lands are you seating the bullets, bullets jammed can give you a spike in pressure, you should measure and work up to the lands as part of the load development?
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