[DonVoigt]

The time that Mauser went to salt blue is well documented, in "The Mauser Parabellum" and else where, it was in the second half of 1937.

There are many serial number lists for 1937 luger pistols that will get one closer to the actual change over if one is interested enough to look for it.

Toggle pins on early("strawed") lugers were indeed heat blued- they were drawn/tempered to the temperature that left the pins blue.

There are lists/commentary in some of the books regarding the temperatures that various parts were drawn to.