Just to put it out there, recently a new rifle was built on an old action and we also experienced a 'fail to fire' with some of the ammo. On close inspection and after lots of debating, it was noted that the firing pin was not quite central to the bolt and so was striking to one side of the primer...some of the primers wouldn't detonate... a couple did causing much consternation. What was frustrating to begin with was that the strike from the pin was a good one! Figuring out how bolts are put together was also a learning curve! Disassembling the bolt and making a new insert to centralise the pin got the whole thing working properly.