I see in Kuhnhausen's "The Mauser Bolt Actions" a table of temperatures using niter bluing that produce different colors- my question is would this range of temperatures, 430º-640ºF, louse up the heat treating on a Mauser extractor?

also, am I correct in thinking the extractor is "spring tempered"?

Spring temper is a little higher than that. The Brits used to use a lead pot to temper springs with. Lead melts near the top end of your tempering colors.

thanks- so, it appears to be safe to use the niter process on an extractor. actually, the colors I would be after are in the mid-range, not towards the top.

the Brits used the lead pot method on cavalry swords, also, around the last 25 years of the 19th century and into the twentieth- kind of a "product needed to match the technology" deal, tempering swords which were undoubtedly on their way out of use.

You can buy all he stuff you need from Brownells and in the bargain learn everything you didn't want to know about nitre bluing..bear in mind it's about the most fragile of the bluing process' Not much more than heat bluing made complicated