January 13th, 2023

Ultrasonic Case Cleaning — Determining the Optimal Dwell Time

cartridge brass case ultrasonic liquid cleaning dwell time brownells

If you read our lengthy article on Ultrasonic Case Cleaning by Jason Baney, you’ve seen the remarkable results that can be achieved with this method, as shown by the photo above. Ultrasonic cleaning has many advantages over traditional tumbling methods of case cleaning. There is no dust or media residue to remove from the brass, and when done right, the cases come out clean and shiny, inside and out, even the primer pockets.

In its Benchtalk Archives, Brownell’s has an excellent article discussing Ultrasonic Case Cleaning. Brownell’s staff compares results, with measured dwell times from 5 to 75 minutes, using both Mpro-7 and HCS 200 cleaning solutions. Tests are performed with once-fired and 5X-fired Tactical 20 (Tac20) cases, as well as once-fired .260 Rem Cases. The article also compares the results from ultrasonic cleaning vs. tumbling in walnut media. Below are Brownell’s results for Tac20 cases with the HCS 200 (non-acidic solution). Go to Brownell’s article for MPro7 results and Rem 260 results.

HCS 200 Cleaning Solution Test

Procedure — Solution was de-gassed for 15 minutes, then 63 Tac20 cases were placed in a single layer, in stainless steel mesh basket. The temperature of the starting solution was 102° F. When the cases were removed the temperature was 110° F.

Once-Fired Tactical Twenty Cases (HCS 200) — Observations
5 minutes: The exterior of the cases are not significantly brighter/cleaner. The primer pockets and case interiors are still dirty.
10 minutes: Exterior of the cases are brighter. 70% of the cases show some degree of cleaning of the primer pockets. Little difference seen inside the case, but case mouths are cleaner.
15 minutes: Case brightness is about the same. Still only 70% of the primer pockets are clean, but a larger portion of each is cleaner. A Q-tip swabbed inside the cases shows that carbon/powder residues are loosening up.
20 minutes: Case exteriors are brightening up. 80-85% of the primer pockets are about 90% clean. The insides of the cases and case mouths are cleaner.
25 minutes: Cases are brighter/cleaner than even new brass. 80-85% of the cases have almost completely clean primer pockets. The inside of the cases are 80-90% clean.
30 minutes: The insides of the cases and case mouths appear to be completely clean. 87% of the primer pockets are virtually 100% clean. 13% of the cases had stubborn primer pocket residue that could not be completely removed.
60 minutes: Eight cases (13%) were placed in the tank for another 30 minutes to try to remove the remaining residue in their primer pockets. Six out of the eight cases were completely clean.

Five-Times Fired Tac20 Cases — Observations
30 minutes: Based on the above observations, I didn’t begin to observe these 5-time fired cases until after 30 minutes: The exterior cases are bright/clean. Brighter than new cases. The primer pockets on 75% of the cases are 75% clean. The remaining cases had primer pockets that were only 25% clean. The inside of the cases appear to be clean.
65 minutes: 25% of the primer pockets were 95% clean, 25% of the primer pockets were 90% clean, 25% of the primer pockets were 85% clean; and 25% were 80% clean.
75 minutes: 75% of the primer pockets were 90% clean.

How Does Ultrasonic Cleaning Work?
The Brownell’s Benchtalk article explains: “Ultrasonic cleaning uses high-frequency sound waves (generally between 20-80 kHz) to remove a variety of contaminants from objects immersed in a liquid. The result of these high-frequency sound waves is a process called cavitation. These high frequency bursts of ultrasonic energy produce a three-dimensional wave of alternating positive and negative pressure areas as the sound wave passes through the solution. During negative pressure, microscopic cavitation bubbles form and will continue to grown until they reach resonant size. As the positive sound wave passes, the pressure rises rapidly and implodes these tiny bubbles. Before these minuscule bubbles implode they store a tremendous amount of energy. These bubbles can be as hot as 10,000 degrees and have as much as 50,000 lbs per square inch of pressure. This sounds alarming, but you have to remember that these bubbles are microscopic in nature and pose no harm to anything, unless you are a carbon /powder residue deposit on a cartridge case!

When this cavitation bubble implodes near your brass case, it transforms the bubble into a jet about 1/10th of its size. This jet of energy can travel as fast as 400 km/hour. At 43 kHz, as is the frequency for our L & R HCS 200 ultrasonic cleaner, this is happening 43,000 times per second. This micro-burst of extreme energy is responsible for removing contaminants from the surface of your cartridge brass. Ultrasonic cleaning can reach into crevices and inaccessible areas and remove surface debris that can’t be cleaned by any other process.”

Photos and quotes © Brownells®, Inc. All Rights Reserved, Used with Permission.

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