The FP's are separate from the hammers in the Flues. They are not in themselves spring loaded. They just slide back and forth it's travel limited by a set screw and a slot on the FP itself.
But, upon firing, the hammer(s) are down fully and under mainspring tension in the fired position. So that tension is also applied to the firing pin(s) when in the fired position.
It is in that position (fired) that you are trying to open the gun up.
What is supposed to happen is that opun the very first motion of the bbls tipping downward is tht the hammer(s) are supposed to retract as well.
That instant retraction releases the spring tension upon the fireing pins which are buried into the fired primers.
With that little bit of release and that it continues to be more released tension as the hammers are cocked and back away from the firing pins by the bbls opening,,the firing pin tips are free to be pushed back as well by the fired case as it is lifted upwards with the bbl.
The case doesn't have the firing pin tip snagged into it's primer so the gun opens easily.
The issue when this doesn't happen as designed is usually the timing of the cocking linkage. It gets worn on a 100+yr old gun and thaat immediate lift to the hammer is delayed.
The bbls can open quite a bit before the cocking linkage engages and starts to lift/cock the hammer.
The result is the firing pin/tip is still embedded into the primer of the fired case and under spring tension from the hammer that has not yet recocked at the same time as you are rotating
the bbls open. The result is the FP is dragged across the primer and off of the case. The gun hard to open. Some can be an 'Over the Knee' to open situation especially if both bbls are fired.
Harder primers can seem to cure the probl. But they just avoid the FP sinking into the primer too deep when fired. So they don't drag as much and the gun opens easily.
The mechanical problem is still there.
