I have had several rifles' metal refinished with KG Gunkote. it involves basic tear down, fine grit blasting, coating with color of your choice, baking, and reassembly. I do not do it, my custom rifle builder does, so I do not have all the particulars on how. I just know it is pretty much impervious to anything. On the bottom metal, depending on the type,, he wil powder coat.
I have had five done and great job. My color: Matte Black.
Smith also builds custom 1,000 yard bench rest from the ground up except for the barrel blank. You may want to look into the "KG"
If interested, he is Chad McCauslin of McCauslin Rifles.
717.258.6607