And in my shop we do lots of heat treat and powder coating etc.. When parts come off the mills or Hobbs we then send them to an outside source for treating. So I'd imagine the firearm world isn't to entirely different. Unless its not cost feaseable to do it in-house, then its outsourced.

Matt, isn't it true Glock Cerakotes their frames in-house and outsources their slides to another company for cerakoting, then the slides are returned for reassembly. I think everyone understands what cerakote is, but the places its being done today is far harder tract. Even some larger gun shops will offer this feature by their staff for a hefty fee. So its a fair question when someone asks who coated it. Now with Sig, you'd expect only the best. But from my own experience, even SIG doesn't want to reveal any trade secrets to even the consumer.

So ill explain cerakote. So you can understand the answer. Cerakote is applied right after final milling and de burring is completed. Once it has been degreased and baked. It is then sprayed while stripped. And then baked again. Once it is cooled it is the assembled. And moved down the assembly line.To properly apply it and for cerakote to endorse your product, it must be applied by a licensed technician. There is only one cerakote school. So the cerakote must then be applied at the factory. Sig and HK used to own each other, weather sig did this in Germany at HK or SIG factories....or if on U.S. soil at American SIG facilities is unknown. But for the process it would be economically prosperous, and better for quality if done at locations where the gun is being built. Sig cannot know wich factory made what gun when everytime. They know batches normally. But they either have a in house technician, or hire out professional help at the construction level before the gun is built. This hold wetheweits duracoat-cerakote- or other like minded substances
-Matt (a former cerakote technician and armorer at a rifle plant)

I called Sig and didn't get much info on who is Cerakoting them, but did learn it will not affect the warranty.