It used so much because if you have the correct machinery you can just dip and de cosmo the rifles relatively fast and easy. However us poor sould without such industrial equipment have to do it manually and its a pain. But if you are a government and need to have a large stash of weapons in reserve you can dip them in hot cosmoline(which is like oil), let it penetrate, and then cool the gun. It is utterly protected from moisture and the elements and only needs to be put with someplace having a roof and it can be left taht way for years at a time.
Good for a communist nation that would put a gun in everyones hand and make them fight at gunpoint i event of a war(like USSR in WW2)
In the day foreign cars used to come shipped from overseas trips with that stuff sprayed all over the sheetmetal, joints, and undercarriage.
Man what a PITA (!) it was to wash and remove that stuff as part of the dealers overall PDI (pre-delivery inspection) process.
One of my first jobs in the auto business was doing this job, removing cosmoline as well as for those buyers that opted for it drilling holes int he sheetmetal and spraying it up into rocker panels as an anti-rust weather treating method.
Messy as hell and tough to remove even with specialized solvent.
i saw something neat on how to clean off cosmoline,
get a trashcan, put a part of the gun (stock, barrel, etc.) with a heating source like a light bulb or torpedo heater, it will heat it up so the cosmo comes off real easy, then wipe it off. real simple....