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How to Properly Remove Cosmoline from Military Surplus Firearms

Cosmoline is helpful because it offers long-term rust prevention, but if you’re a Curios & Relics (C&R) Firearms collector or have ever purchased a gun, you may have what looks to be a mess on your hands. Cosmoline is used to protect the gun against rusting; however, many military surplus rifles were previously submerged in the greasy substance, making its eventual removal seemingly problematic.

Even if your item only has a light coating of older Cosmoline, you might have questions as to how best to remove old coatings. Over time, Cosmoline may have seeped into nooks, crevices, and gaps in the metal but it is actually fairly simple to remove.

Before you start cleaning, here is a list of things you will need:

  1. Acetone, mineral spirits, or kerosene (but avoid the latter when possible, or when your firearm has been painted or blued).
  2. Soap and water.
  3. Shop rags.
  4. Toothbrush or smaller paintbrush for cleaning small, hard to reach spots in metal. Q-Tips and cotton swabs also work.
  5. You can also use a heat gun or an older oven to help “melt” the Cosmoline. There are other ways to achieve this same effect, however.

Some things you should avoid when trying to remove Cosmoline:

  1. Harsh chemical solvents that could strip paint, finishes, or other aesthetic/functional coatings from the gun’s surface.

A note on why you shouldn’t use gasoline: using gasoline to clean a firearm just isn’t practical, especially in the quantity you would need to clean a typical C&R firearm.

How to clean your gun

The cleaning process begins with removing as much of the Cosmoline as possible. This involves two steps:

1. Applying heat to the gun

You can do this by wrapping your firearm in towels and placing it in a black trash bag and leaving it sit out in the sun, or using another heat source—such as a heat gun or older oven—to return the Cosmoline to its liquid state. Attempting to remove the rust-preventive after letting it warm up will turn the Cosmoline into an oilier coating, as opposed to a thicker, wax-like substance. Once you’ve accomplished this, you can move on to the next step.

2. Apply your chemicals

A lot of people swear by mineral spirits as a primary solvent to remove Cosmoline, and you can either apply it with a rag or submerge/dip your gun into it. A sealed PVC tube or large container are both good for soaking guns in mineral spirits, depending on the size of the firearm and container.

You can opt to disassemble your firearm before you start this process or keep your gun intact throughout the cleaning process. Removing all of the Cosmoline will take significant work regardless, so it comes down to a matter of preference. Dissembling can make the process somewhat easier but it isn’t absolutely necessary.

It may take a few dips or baths to get the majority of Cosmoline off. Once you’re satisfied, you can move on to the actual cleaning.

3. Hot water and dish soap

These two things together will help dislodge and remove the remaining traces of Cosmoline, along with a fair amount of elbow grease. Following a wash-rinse cycle will help coax Cosmoline out from all the crevices and grooves, so repeat the process until your water runs clear and you can handle each part without it feeling greasy or oily.

You’ll want to move, rotate, and flex parts to exercise hidden bits of Cosmoline. The more you manipulate, wash, and rinse the firearm, the more you’ll see creep to the surface. At this stage, you may benefit more from dissembling the entire gun or parts of it, like the bolt assembly of a rifle, and letting it soak in mineral spirits.

4. Finishing the job with oil and lube

After hours of scrubbing, you will eventually remove the majority of Cosmoline from the gun—but you can’t stop with that. You have to apply the necessary gun oil, lubrication, and stain (for wooden stocks) to preserve the piece you worked so hard on cleaning up. It’s very important that you get as much of the Cosmoline out of the gun as possible if only to eliminate the risk of having to disassemble the gun to find a hidden chunk of the rust-preventive gunking it up.

The honest-to-goodness proper way to remove Cosmoline from anything, really, is through working at it. Soaking, washing, rinsing, and scrubbing will take hours to complete before you can handle your parts or firearm without the greasy residue covering your hands.