Discovered that the issue was moot to begin with. Even if the spring is not pushing the firing pin all the way back towards the hammer, once you have a primer in there, the primer will do it. On the breech side, the pin does not recess any farther than flush with the breech. So, even if it is poking through the breech a bit (i.e. the spring is not holding it back), the primer will ensure it's sitting flush and that there is plenty of pin for the hammer to smash.