Should not be a problem. If the barrel & parts are slick IMHO you should roughen them slightly to open the pores & etc. 180 or 220 grip paper. I suggest useing Mt. Laural browning & just follow instructions. I use Tru-Brown as that is what I have & am told it works the same as Mt.Laural.
I wait for a day I know it is going to rain for at least 2 days, prepare on the 1st day as the humidity is setting in & brown on the second day. I do it Outside under the awning & can brown a barrel in about 20 hrs. & no sweat box needed. I start about 5am & late that night it is finished. I get a very deep dark chocolate brown.
First thing I do is a swab the barrel liberally with a good gun oil. Then I taper a wooden dowel about 4" long, oil the end & drive it snugly about 1" into the barrel. (Not so tight I can't get it out !) Then I take a allen head screw & plug the vent hole (if removable liner) or a toothpick on a non-removable vent & plug it.
Now it must be clean clean Clean !
I put on new clean rubber gloves & I wash the barrel with Fast Orange, then dishwater liquid soap, then I dry it & spray it all off with electrical cleaner. Now support it on the tang & the dowel, being sure all of the rest of the barrel is touching nothing. Little parts I lay on top of a clean cardboard box.
I apply the browning solution with a cotton ball & Q'tips for small areas, in a smooth even stroke starting with the underside of the barrel, I do 3 flats & turn the barrel over. Just dampen wet it, not running wet & do not wipe it over & over, just one even stroke & quit. Small parts the same way. Wait aprox 3 hrs,scale with a Dixcel Wire Wheel from Borwnells on a drill held in a vice. (special wheel for this) Again, just dampen it, too much solution takes it longer to work.
Reapply the solution & keep doing same until you get a good even brown all over, then do it one more time. First 3-4 applications will be blue, mottled, streaked, really lousy looking, then it will turn around & start looking good & better & then really good.
Remember CLEAN CLEAN CLEAN. If you touch that barrel with your fingers you will have a flaw in the browning. If you pick up Anything but the barrel when browning, you have contaminate the gloves & thus will contaminate the barrel.
One time I moved a gun & by doing so I contaminated the glove with oil, thus the barrel next, had to start all over.
Wearing rubber gloves & leather gloves over that, long sleeve shirt & long pants & shoes. After I brown & descale it, I boil 2 qts of water on the stove with 4 tablespoons of baking soda in each. Bring to full boil then pour over the barrel to rinse it good and while you are doing this have the hot tap water running, rinse the soda water off the barrel. Pat dry with paper towel. Now take some Kiwi Paste Dark Brown Shoe Polish & rub it into the barrel liberally. Get in every nook & cranny. Take the barrel to cool & sit for a day. (Do all small parts the same) Next day a pair of pliers & wiggle the dowel (don't brek it off!) & take out the dowel & vent plug & take a jag & swab the bore with oil. Then take a papertowel or rag & make a lil 1" x 1" pad iof it & put more polish on it & rub the heck out of that barrel & parts again. Do this for 3 days & the stuff is ready to use.
After that you can oil or whatever the barrel, & the polish may come off & so what if it does, main thing is it seals it up good & stops the rust & your gun oil will eventually replace it.
I have done LOTS of barrels and parts with this proceedure & it does work. Only dif I do myself is I bead blast the barrel, but it is not necessary & most don't do that part.
Custom Muzzleloaders & Custom Knives