The whole magic of an inertial firing pin is that the hammer can rest against the slide, and no blow to the hammer can move the firing pin. The pin is actually pushed into the slide by the weight of the hammer, but it is too short to reach the primer. It is actually less safe to carry the gun with one up the pipe and the hammer in the 'safety' notch; in this circumstance, a blow to the hammer can shear the notch, and the firing pin will be sticking out under spring pressure to be smacked by the hammer. It isn't terribly likely that the gun would fire, but it might.
A muzzle down drop is something else altogether; if the gun hits the ground, it stops abruptly, but the inertia of the firing pin might carry it far enough forward to strike the primer and fire the gun. It is long odds of happening, but the firing pin safeties found on guns as diverse as Series 80 Colts or Glocks is to combat this issue.
Another solution is to make the firing pin out of titanium, which is so light as to not have enough energy on a muzzle down drop to fire the gun. New Colt 1911s use this method, as do Ruger LCPs.
Back to the 950 Beretta, which was my EDC before the KelTec revolution. I never felt ill at ease carrying it Condition 2, and the tipping barrel made it really safe to charge the gun without the slight chance of a slamfire when charging an autopistol in the normal way. In order to fire on a muzzle down drop, first you have to drop it, and it has to land on the muzzle...just so. Another one of those 'what can happen vs. what is likely to happen. Not much risk to it.
Now, all that said, two caveats. Some old guns did not have inertial pins, so that a hammer resting on the pin put it in direct contact with the primer. Second, firing pins do occasionally stick in the forward position, making charging the gun pretty exciting....
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