Originally Posted by thndrchiken

How the heck do you figure that?, the 7 1/2 is a bench rest primer which means that the quality control and consistency is tighter for more consistant ignition. It has nothing to do with the cup metal being thicker or being able to handle higher pressure loads. Whoever told you that was just trying to sucker you into buying the more expensive primers. Every single loading manual says nothing about having to use BR primers for semi auto's.