You are running near max loads. Is the OAL allowing the bullet to somehow wedge into the rifling? Are your cases too long, pushing the case mouth into the chamber? It isn't likely OAL is an issue, but expanded primer pockets are a sure sign of over pressure. If you are positive of the charge wt & powder, not sure what would be blowing primers but those two things. Mag primers do increase pressures, not an issue unless riding the ragged edge.

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