while i certainly wouldn't paint any kind of valuable or collecible, i have painted barrels. in this part of the country there is a lot of "shooting matches" involving making bull barrels for shotguns and drill & tap for large scopes. some plate or blue but, i paint. i use rustoleum red primer and rustoleum flat black paint. sand fairly smooth, if you can't do it inside wait for a good warm day & hang barrel till warm to almost hot, dope the wind (unless you enjoy paint fumes and spray-i never did), and put on a good even coat of primer. wait until dry to touch-just a few mins. then use the black. after drying if you don't like results, give'er another shot. have guns done this way that have been painted 5 or more years with maybe a few chips in paint. if that bothers you just shoot on a little more paint. didn't mean to be so windy, have a good'un, bubba.