Ok, let's start working this myth over. It's apparently time for some more myth-busting.
Reading through Hatcher's Notebooks, one finds that he established primer detonation force is in the range of 12 in./oz. for "no fire" to the upper scale of 60 in./oz. for "all fire." This was for 30 cal. centerfire rifle ammo. We'll assume, for the sake of argument that there's no substantial difference between primers of various brands and sizes. The midpoint between the "all fire" and the "no fire" is 36 in./oz. I've just weighed a half dozen firing pins from my parts box and come up with an average of 65 grains, or .148 oz. If we have a free floating firing pin with no spring to impede forward movement, dropping the gun perpendicular on the muzzle from a height of 10 feet will generate almost 18 in./oz.
Again, assuming Hatcher's midpoint of 38 in./oz. would cause 50% of the rounds to fire we'd have to drop the gun, muzzle down, from a minimum of 20 feet. We're approaching Dean's figure of four stories here. Once we add the FP spring to the equation - and my (VERY) informal testing of spring weight indicates a rate of between 3 and 3.5 Lb. So we add 48 oz more to the 36 to overcome the spring and then set off 50% and we're getting into a drop range that's achieved only be mountain climbers and pilots. The same values hold true of falling on the hammer (if down).