The firing pin and hammer is all one piece in the AHFox
The hammer/firing pin can hangup in the fired case if the hammer is not retracting (cocking) fast enough as the bbls are opened.
It's a timing problem.
The quick fix is usually to change ammo to one with a primer that is 'harder' so the firing pin doesn't bury itself as deep into it upon striking the primer.
It doesn't have as far to be pulled back out so you don't feel the drag though there is still some.
Remington primers are often noted to be ones that will cure the problem. Cheddites too by some.
The real problem of timing can be fixed. The hammer(s) have to be started on their rotation back to a cocked position as soon as the motion of the bbls is started downward.
The sliding 'cocking foot' on the center of the bbl lug is often the cause. Sloppy fit in it's T slot and/or excess clearance betw it and the extensions of the hammers it contacts to cock them back.
A simple test to see if the timing is off:
Unload the gun!!
With the hammers DOWN/FIRED, the gun closed, hold it horizontal up in front of you.
Now holding the forend to support the bbls w/one hand, unlatch the top lever w/the other hand but don't pull the bbls down.
Holding the gun closed with the top lever unlatched,,now very slowly let the weight of the bbl's alone drop the the bbl/forend assembly open.
It will open a short distance and then come to a stop/resistance.
That amt that the bbls open when coming to that stop/resistance point is the wear in the cocking linkage.
It can be almost nothing (a good thing) to opening quite a distance, not a good thing
The bbl's are opening that far before the hammer(s) are being picked up by the linkage (cocking foot) and begin to be rotated back.
Until that moment, the firing pin/hammer(s) are still down hard with full released mainspring pressure on the fired case.
The pin(s) are buried in the primer of the fired shell under mainspring tension. At the same time you are trying to rotate the bbl open w/that empty shell.
Hard opening,,doubly hard when both bbls are fired.
You can do the above test with either bbl fired, or both at the same time. Doing one at a time will show if one has move 'slack' in the mechanism than the other.