Typesetting fonts exist in many variations, both modern and vintage. I doubt that a “standard” Fraktur existed. I know when I studied German in college (a
long time ago) all of my textbooks were written in Fraktur, so I usually do not have any particular problem in recognizing the various images posted (when the focus is clear!
). I suspect that there is/was a considerable difference in printed publications and very likely some differences in the official fonts used on German government weapon inspector’s stamps. They very well may have been different depending on the year and/or arsenal (Spandau, Erfurt, etc.).
To my eye, the example alphabet posted by Klaus looks a lot like Old English "Black Letter" font rather than Fraktur.