How to Clean Cosmoline Off Your “New” Surplus Firearm

    So you just bought a shiny new (to you) milsurp firearm, but the problem is that it’s caked in cosmoline, that nasty, waxy, smelly (and supremely effective) rust preventative that just about every military on the planet uses for long-term gun storage. What do you do to get that old gun in tip top fighting shape? It’s really simple!

    I recently purchased a Finnish M39 Mosin rifle still packed in cosmoline and grease, which is a great excuse for me to document the process for the edification of my readers. To start with, you’ll need some things you probably already have unless this is your very first gun:

    • Whatever you need to disassemble the firearm, in this case a set of flat head non-tapered gunsmithing screwdrivers.
    • An oil with which to coat the metal parts; for me Rem-Oil is the height of cheap aerosol convenience, but almost any medium-weight oil will work.
    • A lubricant for the moving parts; I have a tube of TW25B that has lasted me several years so far and will last for many more.
    • Something to hold the gun parts. I will be using a 35″ plastic tub for the receiver components and a smaller plastic box for the smaller parts.
    • Mineral spirits or paint thinner (both are basically the same substance).
    • Plastic gloves, such as dishwashing gloves. I will be using disposable nitrile gloves.
    • A well-ventilated area.
    • A drying cloth.

    I’ve had this tube of TW25B for… A while.

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    There wasn’t enough regular paint thinner available at the store, so I had to also buy “Safer Paint Thinner”, which was a milky color. I just mixed it with the regular kind, and it seemed to work fine.


    Now, the actual process is about as simple as can be:

    1. Completely disassemble the firearm down to its smallest components. Do not take apart assemblies that were not intended to be disassembled, e.g. riveted components.


    2. Set aside any wood components of the firearm. If it is a sunny day, you can set the wood furniture out in the sun to help leech out the cosmoline that may be soaked into them. Do not leave the wood components outside for a long period of time unattended.
    3. Place the metallic components of the firearm into the containers, and take them to your ventilated area.
    4. Put on your gloves.
    5. Pour the paint thinner into the containers over the metallic components.

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    6. Wait for 15 minutes to an hour.
    7. Remove the gun parts from their containers. Make sure that any hollow components like oil bottles are thoroughly cleaned and drained.
    8. Wipe down all the components and apply oil to them; lubricate the moving parts as needed.


      After being wiped down and oiled.

    9. Drain the tubs into a container. Do NOT drain them into the sink or onto the ground! Paint thinner is a hazardous substance and must be disposed of properly.
    10. Reassemble the firearm.

    Beyond that, simply put everything away and dispose of the used paint thinner as needed. Removing the cosmoline on a milsurp firearm is a great way to improve its function and appearance, and to eliminate “sweating” of the stock. Get that nasty crap off there, and enjoy your milsurps, folks!


    My nice, cosmoline-free 1944 VKT M39!


    Nathaniel F

    Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at [email protected]