he he he.
That reminds me of when I took some of that Brownell's Action Magic (a pseudo permanent moly compound) and assiduously doped up the internals of my AR. Immediately after the first shooting session, my Marine buddy went to work showing me how to break the rifle down to clean it, and completely removed the Action Magic. That stuff was a waste of $16.
Obviously the NP3 would be more durable, and it couldn't hurt and it sure would slick up the action. I think, however, your return on investment may well be unnoticed and that it's a solution to a non-existent problem. With respect to the aluminum parts, I think that you could enjoy similar benefits with one of those "phenolic bake-on" sprays that you can get from Brownells.
Thing is, unless there's somewhere for the grit to go, if tolerances are tight, it is going to stay in and carve stuff up. If your coefficient of friction is smaller that's great, but the grit is going to muck stuff up. It is clear from the knife industry that there are no super abrasion resistant finishes. They all wear, chip or flake off at some point
On the outside of the AR, it'd sure be interesting looking.
Also, remember that NP3 is teflon imbedded in a Nickel base, right? PTFE starts breaking down at around 600F, so in rapid fire, that may become an issue for all you blasters.