[Unclenick]

General Pershing was dealing with cupro-nickel jackets that not only fouled but built up lumps. The modern gilding metal alloy isn't nearly so bad, but it still can cause severe fouling in some bores. Since anhydrous ammonia is a gas that has to be kept in pressurized tanks, Pershing's men would not be using it. In anhydrous gas form it doesn't attack copper, anyway, which is how it could be used in refrigeration systems before freon was invented. More likely Pershing's men used what is called stronger ammonia, a supersaturated solution, or else an ammonia dope mix like that Hatcher describes, and which is also known to etch bores sometimes.

In Howe's, The Modern Gunsmith, he describes some pretty nasty mercuric compounds for removing copper deposits. He suggests it is a great money-making activity for gunsmiths, as accuracy complaints were often solved by it in his day. It would be true in some instances today, but not as much as when cupric-nickel jackets were still common.

KG-12 is the most effective modern chemical remover, but it only turns sort of orange tan rather than blue as it reacts, so it's hard to tell when it's done without patching it out, then putting something in that turns blue or green so you can see if the copper is really gone. If you really want to impress somebody, use an Outer's Foul Out and let him be there when you pull the rod out so he can see the copper on it. If the build-up is bad enough it will actually bridge and short and have to be wiped off the center rod and the rod returned before the unit can complete the job.