That’s an incredible question, Ted. I’m unsure. Here's a pair examples of what I’ve read in several spots about the Federal 210 vs Federal 210M distinctions: I purchased 1K for forty five Colt and had the "difficulty". Was just about to surrender on them, and read a post about employing https://federalprimers21016048.dm-blog.com/31940842/considerations-to-know-about-federal-gold-medal-small-rifle-primers