Pete, thank you for sending the pictures, they were helpful in this discussion.
I went out to the shop. First I installed the breech plug and put a spent cap on it and fired. There was a little space, the safety did not quite bottom out. Not near as much leeway as on your mhc but that shouldn't matter as long as it didn't bottom out. I then removed the breech plug and reinstalled the bolt and dry fired. Again, the firing pin did not extend out as far as yours did, but it extends out far enough to do the job in my opinion.
I have come to the conclusion that by being too gentle in closing the bolt I wasn't seating the primer all the way into the breech plug and then part of the force of the hammer blow was spent seating the primer and then not enough force was left to fire the primer. Just like when a #11 cap does not go all the way on a nipple it can take the hammer one blow to seat it and then it goes off on the second strike.
Anyway, that's my story and I'm sticking to it.

Art