I have been hesitant to recommend this, but as you have metal problems with blue finishes as an alternative you could have it Gunkoted Gun Metal Blue. Before you fly off the handle, please hear me out, I have used this for over twenty five years with great results when I did my part. It is my go to finish when someone wants a durable weatherproof finish I can apply myself and repair if needed as In Hawaii getting bluing stuff is a bitch and damn near impossible to get shipped here, along with the hassle of tanks burners and chemicals it is just too much trouble, as I do this work as a favor to my fellow Big Island shooters here as there is no gunsmith. so I do some work if and when I can, and don't charge anyone, anything, so for the locals here it is what I use. I know many view this product as old hat, eclipsed by stuff like cerakote, but with Gunkote, you get a beautiful smooth shiny blue black finish that is chemical and rust resistant. You won't get that wet glass smooth blue black with the ceramic stuff. Put side by side, my 1976 Colt series 70 government gunkoted with gun metal blue, looks just as good as my mint hardly shot 1976 factory Colt series 70 Gold Cup in Colt Royal Blue and that is saying a lot as I purchased both brand new in 76'! Many a person could not tell the difference between the two, but admittedly the finish I did was one of best efforts. I did not mention this earlier as many purist insist on real bluing I understand their preference and why turn their noses at stuff like this as glorified house paint, So be it everyone has a right to their opinion and many people had less than optimum results because of equipment, oil on gun surface, dust, or operator error, but the stuff is durable, not indestructible, it can be scratched by metal. But you can get acceptable results with not much effort, just watch the oil contamination as it is one of the main issues, I once did a 42' Japanese nambu and after 6 times of degreasing and baking to remove all traces of oil, I still had problems until I baked it another 7 times with acetone degreasing ever time. For results like I get, you need the proper spray equipment I use an iwata air brush, A nice compressor setup with proper filters and bone dry air, coming out, you need a spray booth of some kind so you have no dust contamination, and a appropriate oven for curing (made my own) lots of patience and some painting skills (the more the better) but the blue black is beautiful in the end result and virtually chemical and rustproof as it can get and a joy to behold. I'm sure you can find someone that will do a nice job if you don't do it yourself. Just remember, once you bake it to cure, the stuff wears like iron and the only way you are going to get it off is to blast it off if you don't like it.
Best wishes
Aloha One
