[mrerick]

Adding the flutes to the firing pin increased the production expense of the part as the three grooves had to be cut / milled into the original part design.

WW-I production of the Luger at DWM and Erfurt did not incorporate this modification, delivering roughly 2 million military contract Lugers to the Germans and more to other commercial customers - all without the firing pin relieved with flutes.

New features with added expense are rarely added to a military contract without the customer requesting them. "Here - we've got this great new idea to keep the cylinder cleaner so we're adding labor and this cost to the contract to make this change"? Were dirty firing pin cylinders within the breech block ever documented as a problem?

Yet, the grooves were added by the time Mauser started producing them. I think it's reasonable to conclude that the design was changed to solve a problem, and that the additional expense of cutting the grooves was justified by some experience. Until documentation is found specifically explaining why the cuts were added to Luger firing pins, all we can do is speculate.

It is not normal for exhaust gasses to be vented out the firing pin hole of the breech block and through the cylinder inside the breech block that the firing pin rides in. This only happens when a primer is pierced and high pressure gas vents into the hole within a still locked breech.

This is why I think that it's unlikely they were added to solve a fouling or dirt problem, even though it's possible that the grooves somehow helped. With two million Lugers in the field, is it likely that the change was made because of fouling? I'd consider it possible, but unlikely.

But we do know what happens when high pressure gas vents into the firing pin hole of the breech block while the breech remains locked. It drives the firing pin like a cylinder into the spring retaining guide and exerts high pressure against the small locking tab that holds that pin into the rear of the breech. The back of the breech block breaks apart destroying it's ability to hold the firing pin spring guide in place. SAAMI spec today for a 9mm Luger is 35,000 PSI, and something similar would have been driving that firing pin back in WW-I Lugers.

In my opinion, repeated observation of that kind of damage by field and unit armorers would have been enough to justify the expense of cutting the flute grooves into the firing pins. It is a more likely justification than issues relating to fouling. The rear of the firing pin guide fits a bit looser in the breech block than the face of the firing pin, and the grooves would be expected to reduce the striking force and the impulse pattern of the pin against the guide.

This was likely tested empirically by the gunsmiths at Mauser and found to be slowed and reduced enough to stop the cracking of the breech block area that retains the spring guide. The timing of the movement of the firing pin could have been delayed slightly allowing the breech to unlock before full pressure was applied to break out the firing pin guide tab retention. That is, of course, speculation - but it could be tested and verified today.

Until documentation is found, this has to remain speculation. I think that the patents Dwight pointed out in the earlier posts do inform us on why the feature was designed.