TFB Armorer's Bench: Cleaning Cosmoline With an Ultrasonic Cleaner

Welcome everyone to the TFB Armorer's Bench! I recently spotted a Sten Mk2 kit for a decent price and couldn't resist picking it up. These kits used to be available for a couple hundred bucks, but lately they've shot up in price as they've become less and less common. People buy these because they're simple to bring back to life in semi-auto form with some new parts and a little know-how. It seemed like a fun project. Mine arrived soaked in thick cosmoline in a plastic bag, which turned out to be the perfect test case for the RCBS Ultrasonic Cleaner 2.

More TFB Armorer's Bench:

• TFB Armorer's Bench: RCBS Ultrasonic Case Cleaner 2 – A Closer Look
• TFB Armorer's Bench: Mounting an Optic on an X-Frame Revolver
• TFB Armorer's Bench: Diagnosing and Assessing a Winchester 94
• TFB Armorer's Bench: Diagnosing and Assessing a Colt 1877 Lightning
• TFB Armorer's Bench: By The Armorer Book – M1 Garand Maintenance
• TFB Armorer's Bench: How I Make Dummy Rounds

TFB Armorer's Bench: Cleaning Cosmoline With an Ultrasonic Cleaner

Here, we at TFB hope to inform, entertain, and even inspire any would-be gunsmith or armorer out there. Ideally, with the information I provide and with the help of our sponsors, you can have some useful knowledge pertaining to the conservation and improvement of firearms technology while at the same time sharing experiences and teaching each other new tips and tricks along the way in the comments. Digging deep into what it is to be an armorer or gunsmith has significance but what is important is what those people do to show they’ve earned that title. I am happy to share my experiences and knowledge and hope it is informative!

Make your personal safety a priority:

1. Practice proper gun safety. Always make sure before the firearm hits your bench that it is unloaded and safe to be handled.
2. Wear the proper safety equipment. The main one would be safety glasses (decent ones) since parts are often under spring tension and you may work with high RPM tools. Other honorable mentions would be latex gloves or a respirator when working with potentially harmful solvents and oils. Also hearing protection when working with loud machinery or test-firing firearms.
3. Modifications, alterations, and customizations will void your firearm’s warranty 9.5 times out of 10. Please take that into consideration before attempting any at-home gunsmithing.
4. If you are unsure about proper safety practices, disassembly procedures, or warranty standards, stop, put down the tools, and consult a competent gunsmith.

Quick Background: Cosmoline and Ultrasonic Cleaning

If you've never dealt with cosmoline, you're ahead of the game. This thick, waxy preservative shows up on old military surplus guns and parts kits. Sure, it keeps metal from rusting for decades, but removing it sucks. You end up fighting with harsh solvents and scrubbing until your arms hurt.

Why This Test Made Sense

I wanted to see three things with this project. First, I wanted to find out if an ultrasonic cleaner was actually capable of removing cosmoline, or if it would still be a by-hand-plus-heavy-chemicals situation. Second, I was curious how the cleaning solution would hold up to this kind of abuse and whether it would still be usable for future projects. Third, I wanted to see if the RCBS system could handle this kind of challenging job while gaining more experience with the unit.

This fits into my broader plan to test the RCBS cleaner on various applications – I'm planning to do more generic cleaning with it, suppressor cleaning, and brass cleaning in time. But cosmoline removal seemed like a good stress test to start with, especially since it would let me avoid exposing my hands and lungs to harsh solvents if it worked well.

The Setup Process

I used the  RCBS Weapons Cleaning Solution diluted with water at the recommended 40:1 ratio. The plan was to set the temperature as high as the unit would go – that's 60°C or 140°F – and run 30-minute cycles. I figured the cleaner would do all it could accomplish in that timeframe between manual scrub sessions.

The major issue I ran into was heating time. The unit takes a very, very long time to heat up to any meaningful temperature. I'm talking an hour or more, and it never actually reached its maximum temperature before I ran low on time and had to proceed anyway. You're much better off dumping in hot water and mixing your solution each time, though this sucks if you don't want to waste solution from a previous run – you're stuck with cold or room-temp solution that needs heating time.

Results and Observations

Compared to traditional cosmoline removal methods I've used in the past, this was already winning just by avoiding harsh solvents. I usually resorted to aggressive chemicals when I was in a rush, but if I didn't have to expose my hands and lungs to that stuff, the ultrasonic method had a major advantage right there.

The cleaner surprisingly got at deposits I couldn't reach manually. The cavitation action worked its way into tight spots and complex geometries that would have required disassembly to clean properly by hand. Parts came out looking significantly better than when they went in, and the final wipe-down was much easier than expected.

Cleanup was actually pleasant thanks to the drain spout. Being able to wipe down the inside of the tank and easily empty the solution was convenient. I ran the drain hose through a piece of thick cloth to see how dirty the solution would get, and I was surprised – it wasn't that bad. This told me the cosmoline had more or less dissolved into the warm solution rather than just floating around as chunks. Since it would likely redeposit later in some form, I decided to throw the solution out rather than try to reuse it.

Practical Takeaways

I'd definitely recommend this method to others dealing with cosmoline, especially as an alternative to harsh chemicals. The process is much more pleasant than traditional solvent-based removal, and the results are genuinely good. However, there are limitations – mainly the vessel size and the heating time issues.

As for my overall impression of the RCBS system, it's proving to be capable equipment. I love the drain setup and the solution measurement features. I'm not a fan of the buttons that use only symbols rather than words – I have to memorize what each one does or consult the manual. The unit is noisy, like every ultrasonic I've used, which is expected. My biggest wish is that the actual tank was bigger, since the overall system is seemingly giant, but the usable space feels limited.

Conclusion: Cleaning Cosmoline With an Ultrasonic Cleaner

Cleaning cosmoline with an ultrasonic cleaner turned out to be a viable alternative to traditional harsh chemical methods. The RCBS Ultrasonic Cleaner 2 handled the job well, though it revealed some limitations in heating time and tank capacity. For anyone dealing with cosmoline-soaked surplus parts, this approach offers a much more pleasant working environment while delivering solid results.