[ithacaartist]

Welcome, Doc. A low-viscosity petroleum product of any kind will do the job. PB Blaster, Liquid Wrench, CRC all penetrate fine. Even plain old kerosene is just about as good. Don't get anything water-based near it, which risks actually harming the remaining blue. I'd go so far as to use an oiled toothbrush to get down into the pits, but change the solvent often, to avoid finish damage. Iron oxide is abrasive, and you don't want to rub the surface with it if it can be at all helped. You'll know when you're finished cleaning because all the red will be gone. That's the rust that is still active.

I seem to recall that 1916 DWM-made Artilleries are nowhere near as common as, say, the 1917s. Depending on what you have invested, it might be a case for restoration! Let's see what others say...