The only times I ever got a delayed fire from any primers was when I was using double based powder Reloader-22.I had bought some Sellier&Bellot large rifle magnum primers and was trying them out in a 300 Win Mag.I was getting about a half a second delay before the rifle fired.It did the same thing with some CCI 200 large rifle primers.One of the one's using the CCI-200's failed to fire.I pulled the bullet when I got home to see if the primer had ignited at all and found the powder was blackened but none had ignited.I don't know,maybe the double based powder needs a hotter primer.Never had any issues with this rifle or lot of powder using Winchester large rifle magnum primers.The S&B and CCI worked fine with single based AA-4350 and Ramshot Big Game.