Sorry, I fat fingered the previous reply. What I mean to ask was if that is rust I see on the gun, links and ammo (the brass looks corroded).
The Feedtray cover and barrel look good.
The mount... Not being Navy, it it unfamilar. That appears to be a special iron 4 coating.
The ammo: OMG!
Maybe the photographer found it somewhere?
All are corroded. The corrosion on the steel portions is commonly called rust. The bluish colored powdering corrosion on the casing and projectile is typical of copper alloys (brass) corroding.
3 basic oxides of iron (rust)
Ferric oxide Fe2 O3 (red)
Ferrous oxide FeO (black)
Iron oxide Fe3 O4 (black)