From what I have read, reloading 223 for a AR a magnum primer is needed to prevent accidental fires when 'sending the bolt home.' in my manual (Lyman's 49th) they use a Remington 7 1/2 primer and from my understanding it is not listed as a magnum. I have read a lot of stuff saying it has a lot of the same qualities and will work. What do you guys think? Thanks for the help, I'm still a newbie trying to figure this reloading stuff out.