I get a soft soldered double every now and then.These guns frequently have dissimilar metals, mostly various CM parts.Is there an easy method to produce a nice rust blue or similar looking finish?I do have a long tank to heat water or whatever.
Any help would be greatly appreciated.Thank You

There's a lot of rust blue solutions out there and I've used a few. Laurel Mountain is user friendly. Check it out here:

http://www.laurelmountainforge.com/barrel_brown_inst.htm