Originally Posted by Iskaryot
That sounds good in theory, but doesn't it also expose it to the elements? I guess it would only matter if it's made of steel when it could rust.
Not just steel (some steels won't rust, such as stainless, or treated steels.)
Die cast zinc-aluminum will also suffer from oxidation, particularly if it has a higher zinc content, it will pick up a dull/dark grey oxidation that looks really ugly. Be prepared to re-do the polishing every couple of months to take off the oxidized layer if you decide to do this to most airsoft barrels, as the majority of production grade barrels (such as what KWA offers) are made from pot metal. Even Tokyo Marui's metal parts are highly susceptible to oxidation, as anyone who decided not to heed similar advice will eventually tell you. You could
seal it with acrylic to protect it from the elements, but it will eventually wear down due to contact with the slide and its basic mechanical function. The required upkeep isn't worth the cosmetic benefit, in my opinion, as well as the devaluing of the gun/component.
Also, be aware of any coatings that you add on, as the added thickness could affect tolerances and cause mechanical problems.