Gass relief hole botom of breech block.

[HisSoldier]

Doing this simple gas relief hole in two of my P-08's that for sure aren't collector guns I discovered that the Mauser 1970 4" 9MM pistol's firing pin is fluted full length, well, more correctly, it has a relieved or reduced band around the center leaving slightly larger circumference at both the front and rear ends (As all P-08
FP's have).

BUT these full diameter bands (front and rear) each have 3 very shallow grooves at 120 degrees and only a few thousandths of an inch deep (Shallow like rifling grooves engraved on a bullet, but straight) so that one could assume the intention was to allow gas to escape past them, OR, to just reduce the area of the OD to minimize friction perhaps.

They clearly won't act as pistons during a ruptured primer.

This was a total surprise to me as I only knew of the cylindrical firing pin devoid of reduced features or the later grooves that only go not quite half way toward the back. I should have snapped a photo I guess.