As a former operator of one of these, the M2 appears to be fairly clean. I'd say it has too much oil, but maybe that's a navy thing. That much oil would attract a tremendous amount of dirt. It's not uncommon for the metal components to be different shades as they are commonly replaced. As for the ammo, I probably wouldn't have loaded that box of .50API into MY M2, but I can say that as a WWII machine gun design that just doesn't get any better, it will likely still shoot. The rust below the barrel is actually on the gun mount, not the gun.
yeah- i just realized that's probably an army pic- sorry- i saw all the stuff in the background and immediately thought it was on a ship or something. embarrased!
The rusty spot appears to be on the gun mount and not on the Ma Deuce.
When you're right, you're right.