If the "grease" is really cosmoline, which guns used to be commonly stored in, then the easiest way to clean it is with a large dose of boiling water.  Use a large teapot or something bigger, an pour lots of boiling water over the metal items that need to be cleaned. Cosmoline comes right off with boiling water, and the heat of a large dose of boiling water will actually dry the metal. A little bit of water might need to be wiped off, and you should run a patch through the bore, but it is rather amazing how thoroughly hot metal will dry itself.