One of the most durable finishes possible is ordinary oil-based Rust-oleum paint.
I use a mix of flat black and a bit of gloss black, applied with an airbrush, and baked in the oven.
Straight flat black looks nice, but as you handle it, it tends to get shiny areas that give it a blotched look. To prevent this, either find a satin finish Rust-oleum or mix 6 parts of flat with one part gloss, more or less, to your preference. This gives a flat finish that won't blotch.
After degreasing thoroughly, spray on as thick as possible without having sags or runs. Allow to stand about 1/2 hour to tack up, then bake in your oven at about 300 to 325 degrees for one hour.
(DON'T do this when your wife is around, it makes the kitchen smell).
Allow to cool and stand over night to harden completely, then coat with lube.
Paint is what many AK makers use as a finish, and it's an amazingly sturdy and good looking finish.
