Have you guys disassembled your bolts and noticed how stiff the firing pin spring is? I had the same misfire problems on slugs last year during hunting season. I took apart my bolt and that firing pin spring is crazy stiff!
Any misfire I ever had was either due to the brand of cartridge, or because I had short stroked it.
The firing pin spring is really strong. When pressing it with your finger, you'd wonder how the hammer manages to push the pin forward with enough force to dent the primer at all.