To not hijack this thread but a colleague of mine that produces ammunition implies the Federal 210M primer. Why, I have no idea as he was seeking not to present me proprietary information. I will utilize the Lee Hand Priming Software Once i get around to using the Feds. Ken, https://federal-primers-21043208.blogpixi.com/32130711/the-best-side-of-federal-large-rifle-magnum-match-primers