Originally Posted by
LaneNebraska
The 17 rem, 204 ruger, 222, 223 all need the thickest/toughest primer because of the very high pressures involved in small rifles. Theses same rifles in semiauto/AR-15 configs are even at greater risk of Slam-Fires caused by the floating firing pin. The proper primers were specially designed by Rem are the 7 1/2's.
These are thicker and resist firing pin punctures and slam-fire ignitions.
You may be able to get by with(6 1/2's) bolt action rifles and moderate hand loads, but I wouldn't do it.
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.