@Zonie is spot on.
Moose Milk is a mixture of water soluble oil and water. The resulting emulsion is milky in appearance and is slick. Depending on who mixed it and for what purpose, Moose Milk can be used as a cleaner, patch lubricant. The main difference is in the ratio of oil to water and the oil that is used.
@painter's Moose Milk takes advantage of the PineSol and water to clean the fouling Its the same for the Moose milk that
@TexasAndy uses as he cleans his revolver. I use my mixture made using an old formula of NAPA cutting oil and water to lubricate patches. Whether you use cutting oil or Ballistol makes little difference. A mix of from one part oil to 5 to nine parts of water is a good patch lubricant. Add some rubbing alcohol to keep it from freezing in the current cold weather. Add a squirt of dishwashing soap to your mix and it is good as a patch lubricant and to dampen a patch for wiping the bore between shots or cleaning fouling off your revolver before reloading a cylinder.
A mix of one part water soluble oil to seven parts of water can be soaked into your patching material and when you let the patching dry flat, you have a good dry lubricated patching material. Couple the dry lubed patch with the same ratio of "Moose Milk" used to wipe the bore between shots is highly thought of as a very accurate target procedure.
There is another variety that uses a mix sometimes referred to as MAP and by others as Moose Milk. This is an effective cleaner. Its made of one part of
Murphy's Oil Soap, one part of rubbing
Alcohol (70% or 90% makes no difference), and one part of 3% hydrogen
Peroxide. When this mix encounters fouling it makes an impressive amount of foam and really cleans the metal. While there are concerns that the extra oxygen in the peroxide encourages flash rusting while cleaning there are many who really love it.
Ultimately there are hundreds of Moose Milk recipes and those that use then swear by all of them and think anyone who uses any other mix need to get better educated on Moose Milk.
Oh, and when I shoot my percussion firearms, I remove the nipples.