When were unfluted firing pins modified / replaced ?

[Edward Tinker]

I find that most 'early' Simson's are non-fluted, but the vast majority seem fluted to me. My gut feeling (but I have never kept track) is that shortly after production (1925/1926), so mid 20's the requirement for fluted came into existence.

I also seem to remember a directive, that maybe discussed this.


Ed