We have powder coated quite a few firearms in the past but it does have it's problems. We apply it over our "regular" Tuff-Gun 1 (TG-1) finish and call it TG-2. It does work well but like I said: It does have it's problems. First, it can't be applied to any close tolerance parts and not to any internal surfaces. It's to thick and will not burnish. The thickness problem is obvious but the burnishing problem only shows up after the firearm is reassembled. Burnishing in this case means that the finish will wear to match the part next to it. It does not "break in" very well at all. Our TG-1 finish uses Gunkote 2400 Series as the color coat. It will wear to a perfect fit on the parts that move against each other. In fact, I purposely apply it thicker to some areas like slide rails, etc. so that it has "room" to burnish properly. Powder coat will not burnish, it will just break! There are some other finishes like duracoat that also will not burnish and have the thickness problems but that stuff is easy to remove.
The second big problem with it is that it's not really very good at withstanding high heat. (Yes, they make powders that are heat resistant) I applied it to an AK barrel and then went to the range. After two mags at rapid fire, the powder coat on the barrel had changed colors and was smoking.
Now having said all of that: It does work well on non-moving parts like bipod outer legs, slow firing barrels, bolt handles, etc. but it's worse than no good on close tolerance moving parts. Removing that stuff takes a LOT of work!!
As other posters have said: It's applied as a very fine powder. The part being powder coated
MUST ABSOLUTELY be 100% masked off to keep it from drifting to the inside surfaces. That's why I will not apply it to pistol frames, rifle receivers, etc.. There's just to many openings for that stuff to get inside.
Another problem with it is that it can have "leakage" meaning that if moisture gets under it, it will rust the metal before it flakes the finish off. That's why I apply it over our TG-1 finish so the metal has that protection from adverse environmental conditions.
Overall, it is a good finish for firearms as long as it's properly applied by somebody that knows what NOT to powder coat! Keep yer powder dry, Mac.
(That's not a pun. It's the way I sign my posts!)
Tuff-Gun Finishes. The Name Says It All.
Mac's Shootin' Irons.
http://www.shootiniron.com