Please understand I'm not a chemist (though I have spoken with real chemists at different times on this subject), so I will be using more common terms in this post.While this "oil" post is still active, I've got a guestion on lithium grease. I've noticed that there are differant colors of this grease.Some white, black in my grease gun. Is any old grease like the stuff fresh out of the grease gun safe to use on a firearm? Such as putting a dab inside to coat the bore? Then what about the one with " Moly" in its contents? Remember no one is advocating gobbing the stuff on, just a small fingernail size dab (or smaller) of grease inside the bore. Would it be difficult to remove before the next shooting?
"Gun Greases" are usually broken down into two categories, one for long term storage and the second for lubrication of operating parts.
RIG Grease is well known for long term storage to prevent rust. It works marvelously well, though it requires a solvent like Stoddard solvent, mineral spirits or other types of solvents to remove and then the metal is oiled for shorter term rust protection. IOW, soapy water we usually use on ML Guns, doesn't do a very good job of removing it. The main useful property of grease is it stays where you put it better than oil over long periods and usually put on thicker than oil, to better resist the air and other elements from attacking the surface metal.
Gun Greases used for lubricating operating parts is mainly used for lubrication of the metal parts when operating at fairly high speed. As an example, Oil is used as a preservative for the metal parts on M1 Garands and Carbines, but you need a thin coat of grease where there is metal to metal contact of the operating parts, to reduce friction and wear. Now, of course with Muzzle Loading Guns, most of the parts don't operate at high speed and because of that, then Oil is mainly used as both a preservative and a lubricant. However, I like to put thin coat of grease on the axis of a tumbler, on the sear screw and a couple other places to prevent wear, though NOT on the full cock notch of the tumbler and sear face.
"Moly" is short for Molybdenum and is an additive to greases used for high pressure and added lubricity for metal to metal contact at higher speeds. They began adding it to G.I. Gun Grease in the late 50's/early 60's in the brown color G.I. Grease that came in the O.D. colored cans many of us remember from that time and into the early 70's. Later in the mid late 90's, they changed G.I. Grease back to an off white color, but it still has Molybdenum in it. Again on muzzle loaders, I only use grease in applications like I mentioned above and that also goes for some parts of BP revolvers.
BTW, one doesn't need to buy "Gun Grease" (other than RIG) for most applications. Modern Wheel Bearing Grease, with NO fiber material in it - that most modern greases no longer have, is every bit as good. I got that from "The Lab Boys" at both Rock Island and Albany Military Depots while I was the Division Ordnance Chief for 1st Marine Division in the 1990's. Since we could be in places where supplies might not catch up to us and we had run out of the "approved" cleaning/preservative oils or greases, I asked what we could use instead. They also informed me that diesel fuel would be great to use as a solvent and cooking oil as a preservative for small arms, when approved items were used up. Of course the Military is not allowed to use those things EXCEPT when the approved items are not available.