Most likely a hangfire is due to a gunked up sear stop or the trigger actuator rod. The hammer, under pressure from the spring is being blocked at the sear OR the trigger mechanism is being blocked before it can actuate the sear block.

Pull the trigger and the sear stop clears the sear, allowing the hammer spring to actuate the now released hammer. Once that hammer has spent the energy created by the spring, the firing pin cannot store energy. It is a free sliding component (in most modern firearms, your mileage may vary).

Look to the trigger assembly or the sear/sear block assembly.

My $.02