To not hijack this thread but a pal of mine that provides ammunition implies the Federal 210M primer. Why, I have no idea as he was hoping not to present me proprietary info. I will use the Lee Hand Priming Resource when I get around to using the Feds. Ken, https://federalprimersammunition89123.thekatyblog.com/30860081/federal-large-rifle-magnum-match-primers-for-dummies