I own a model 25 MN and have shot aseveral hundred rounds through it most of them being CCI Maxi-Mag's, andI have never experienced the first misfire of any kind. I would bet it was the shells if the firing pin hit in the right area, and it was deep enough it would have to be the shells. Don't give up on the Maxi-Mag shells, unless you continue to have problems with other boxes of shells.