This is also the same reason that many people think their misfire has to do with a weak primer hit, because they look at the unfired cartridge, and see a smaller dent than usual in the primer than usual, which the large size of the dent in a fired cartridge is caused by the recoil throwing the primer face back against the pin in the microsecond of the pin strike.
In agreement with about about case movement before pin reaction. You can seem the same thing sometimes in revolvers, but instead of a smear like on semi autos, there is a double strike marks on it from the pin and case moving in relation to eachother, when the primer is hit, the jump of the cartridge before it seals make it hit in a different spot. Though in revolvers it can mean a problem such as cylinder looseness or hangfires.
