Primers are one of the least understood items in anyone's reloading kit. Shooters are amazingly ignorant of the things, even though in threads like this one, posters claim how knowledgeable they are, but they are nothing but confident idiots about the things.
Firing pin strike
http://thefiringline.com/forums/showthread.php?t=527973&highlight=primer+offset
This was written by a CCI employee and it totally confounds a number of the schizophrenic ideas floating around in the shooting community. Once of those schizophrenic ideas is that "high primers" cause slamfires. High primers are in fact, about the least likely cause of slamfires.
I recommend reading
Mysteries And Misconceptions Of The All-Important Primer
http://www.shootingtimes.com/2011/01/04/ammunition_st_mamotaip_200909/
As the article states, high primers are the most likely cause of misfires! A couple of conditions have to be met for a primer to ignite. The first is that the anvil has to be firmly seated. If the anvil is dangling in the air, the primer will not go bang. Often you read posts where the reloader is able to make the primer ignite a second time by recocking. What has happened is that the first firing pin strike has seated the primer, set the gap, and the primer goes off when hit again. The second condition is that the gap between primer cake and anvil have to be set. If the primer is pushed too hard, I am of the opinion that the anvil can crack the primer cake.
So, lets say your primer is high and your firing pin struck it. You could have cracked the primer cake without the primer igniting. You also could have cracked the primer cake from an off center firing pin hit, which was the discourse that produced so much of the angry ignorance in the referenced post. Off center firing pin hits increase the chance of a misfire, and the further the firing pin hit is from center, the more the misfires increase. At some off center distance, the primer will not ignite, again something not acknowledged by the confident idiots in the angry ignorance thread. If the primer cake cracks due to off center hits, the primer will dud out and not ignite no matter how many times the thing is hit with the firing pin.
Lets say the primer cake cracked, well it still is the combustible compound that it ever was, and if you apply heat, it will go off.
I have had primers misfire due to weak firing pin hits. In a different mechanism, some have gone off, others have not. I assume the primer cake was cracked on the first, weak, hit.
Something else, I have had dud primers from all brands and types. At least I cannot think of a primer brand and type where I have not had at least one dud primer. I don't know if it was my fault, due to improper seating, like seating too hard, or too soft, or if the primer was a dud from the factory. Now that I think of it, I have had factory ammunition that would not ignite, particularly rimfire ammunition. So, bad things happen.
