Quote Originally Posted by pocketshaver View Post
Always see in the old US Military shooting manuals for springfield rifle to use cosmolineicon to put a thin layer of bullets when shooting for maximum accuracy or large amounts to help reduce cleaning effort
The grease used on bullets by U.S. shooters was 'Mobilubricant', in the early days of the 1903 in match competition. The purpose was to help prevent metal fouling from the cupronickel jackets of the original M1906 ball ammunition. The CN tended to leave lumpy patches in the bore, which was very detrimental to accurate shooting and difficult to remove. The grease was applied with a little device called a 'spitzer greaser', which was a small tin can with a snug fitting washer in the top. The washer had a hole just large enough to permit insertion of the bullet up to the neck of the case, and pressing downward on the washer insured that the bullet received an even coat of the grease. The lid was kept on the can between uses to prevent the entry of dirt and grit. With the adoption of gilding metal for bullet jackets in the mid-1920s, the need for grease disappeared with the metal fouling problem. Cosmoline, or cosmic, is a compound of vaseline and rosin, which is an excellent long-term rust preventive, and was never used for lubrication of either mechanisms or bullets. In fact, because of the rosin content, it makes a rather excellent flux, which can actually cause bullet jacket material, including gilding metal, to sort of 'solder' itself to the rifle bore, if the cosmoline is not thoroughly removed before firing: I've seen several instances of this problem over the years.
That aside, oil or grease in the chamber or bore of a rifle is undesireable, because it prevents proper expansion/adhesion of the cartridge case in the chamber, raises chamber pressure, and increases backthrust on the bolt, though there have been a few rifle and machinegun designs which require oiled cartridges to insure proper function and extraction - those are rare, and no modern sporting or military rifle requires or would benefit from oil or grease in the chamber or bore.

mhb - MIke