The semi-automatic shotgun is arguably the perfection of the gun as a firearm.
I spent my youth alongside my dad in the Mississippi Delta as he and his Belgium-made Browning Auto-5 kept every Thanksgiving, Christmas and Easter properly stoked with wild turkey.
You could find something restricting either the trigger from being pulled safety or movement of the sear to disengage the hammer.
Failure to eject after a scope was mounted is a situation that can also be encountered.