That's one of your problems!
I have a buddy who had problems with the CCI-400 series slam firing on him. After a little research we found out the way to go is CCI-450 Small MAg Rifle Primers. CCI-400 are designed for the small rifle caliber bolt guns, and the 450s have thicker cups. If you really want to tune her up get some CCI 41 primers. These are OEM CCI MILSPEC primers. They come in a white and black box with CCI 41 on them. This is what the military manufacturers use on military contract ammo. It's a heavy cup and won't slam fire.