Is there a way to apply a new coating?
From what I have read, the FN firearm is a delayed blowback action. High pressure delayed blowback cases have to be lubricated one way or another, just as LTC Chinn states in his book, The Machine Gun Vol IV
Prior WW2, these mechanisms were oiled, such as
or the rounds were manually greased, such as the rounds for the Oerlikon machine cannon.
You can see at exactly 2:14 on this WW2 video a Sailor’s hand painting grease on the 20 mm ammunition loading machine for the Oerlikon anti aircraft machine guns.
this is a deck mounted Oerlikon
the Pedersen rifle used ceresin wax
It is my opinion that leaving a thick layer of resizing lube on the case will provide all the lubrication necessary for proper function of a P90 PDW. Or a light grease, making sure that the neck and shoulder are greased.
this amount was more than enough to fireform 300 H&H brass
I think the secret sauce that FN uses, is a sintered teflon coating. These clear coatings go way the heck back, as the Navy was trying to eliminate the pre greasing of the Oerlikon rounds. You can imagine, a greasy round attracts dirt, makes a red hot machine gun even smellier, and it takes time to grease rounds. I found the Navy tried all sorts of dry lubricants, including ceresin wax, and chamber flutes, before tossing in the towel and installing an oiler on the top. A bud of mine used an Oerlkon with an oiler on his river barge in Vietnam. His fellow river pirates stole the machine cannon from an Air Force base and bolted to the deck of their barge.
some of the history behind sintered teflon coatings.
“Thin Films of Polytetrafluoroethylene Resin as Lubricants and preservative coating for metals, May 1958 Industrial and Engineering Chemistry. V.G Fitzsimmons & W. A. Zisman US Naval Research Laboratory
https://pubs.acs.org/doi/10.1021/ie50581a033
Application to Ammunition.
Thin coating of Teflon are remarkable dry-film lubricants for cartridges. In 1951, gun firing tests using brass cartridge with one coat of clear Teflon suspensoid revealed excellent performance and freedom from gun malfunction. After much cooperative experimentation with the du Pont Co., Teflon coating were developed with excellent adhesion to brass and steel and greatly increased corrosion resistance.
Coating with satisfactory resistance to rain, humidity, and salt water spray had to comprise tow or more coasts having a total thickness of from 0.00005 to 0.0007 inch.
Exhaustive firing tests with coated steel and brass 20-mm cartridges established the superiority and greater reliability of Teflon over other lubricants. Contract pilot-scale production studies by the Army and Navy have since developed satisfactory methods for the mass production of Teflon coated cartridges. 
