When trying to get a two-tone look on a fluted bolt, color on the bolt and raw milled in the flutes. Does the bolt receive the color first and then get milled? Or does the milling happen first and the flutes are somehow masked off and then the color goes on? I asked same question in custom forum but probably more fitting here. Thx.

You can do it either way. Same thing for fluted barrels.

Done properly, Cerakote is far and away the most durable of the spray on finishes but not worth getting tooled up for it unless you plan to go into business. The do it yourself guy with less than 30 jobs will be money in the bank to farm it out to a Certified Pro with a warranty. Obtaining the 100 grit aluminum oxide can be difficult to get and last time I bought it was $2 a pound. I had to drive 450 miles to get it. Acetone was $80 for 5 gallons. Neither of these products can be reused. People do it but sooner or later the durability of the finished product will be compromised.