Wow. Someone still shoots cupro-nickel jackets (silver/gray colored alloy)? I was trying to remember when the military dropped it for the modern 5%:95% zinc/copper gilding metal? The fouling problem was the reason for the change. Typically, match shooters reported accuracy loss in as little as five rounds owing to the lumpy fouling it makes that builds on itself. I have no clue how machine guns dealt with it? Old timers would grease those bullets.
I recall reading that the 1921 National Matches debuted cupro-nickel with tin plating, something Col. Townsend Whelen came up with to reduce the fouling. I also seem to recall Hatcher mentioning that some old timers at that match insisted on greasing the tinned bullets despite warnings not to, and that resulted in a couple of burst guns. I don't think those tin bullets were around for too many years, so the military must have switched over not terribly long after that.
Howe's 1941 edition of Modern Gunsmithing also included several formulae for removing the old jacket fouling, but I recall they included some pretty hazardous mercury compounds. The bullets were probably around and used by handloaders for a long time after the military changed over. Howe listed removing that fouling as a profitable activity for gunsmiths to restore accuracy to guns.
These days I would opt for the Foul Out electrolytic cleaner over harsh chemicals for really heavy fouling, just for handling and disposal reasons. The Foul Out patent has expired and you can check out a build-it-yourself design along with other copper removers at
Father Frog's web site.