Series 80 guns have a firing pin block incorporated into the slide assembly. The block is in the form of a spring loaded plunger and prevents the firing pin from traveling forward under inertia should the pistol be dropped muzzle first onto a hard object, ie; ground. The plunger is pushed up and out of the way by a cam in the frame. The cam is actuated by the pressing of the trigger.
I hope I explained that correctly.