Has anyone used these, and if so what kind of performance have you had with them? I ask because tomorrow I'm going to pick up a few thousand. I've heard the cups are very hard, and can cause misfires in some rifles. They are harder to prevent slam fires, but I've never heard of an AR-15 having a slam fire. A Ruger Mini 14 perhaps, but again I've never heard of any. Are these things a solution to a non existent problem, or is there a valid reason for their use? Thanks in advance, Bill T.