Cerakote would be great.

For something you can do at home, Boeshield or Eezox.

you know what? I once did a test where I used car polish on a scrap rifle barrel and posted pics of results on Gun Site.
I polished with that Liquid Diamond stuff on one piece and nothing on other piece. it was not a huge discovery and major break through result, but it certainly worked well enough for hunting bushpig for a week in sub tropical coastal bush. I spiraled a length of tape around  the  barrel and the applied and polished the polish, and ended up with a polished - unpolished spiral around barrel. After the 4 day hunt, it was clear what was treated and not treated.

My next test, threatened for like 10 years now, is to test shoe polish as a surface protector, apply as with shoes and polish up - obviously the Kiwi type wax sealant polish. Perhaps even stoep polish would be worth testing.

Thanks Treeman, I'll give it a try.