I tumbled three different types of brass in walnut media (PPU 308 Match, PPU 7.62 NATO and MEN 7.62 NATO) till it was nice 'n shiny, then decapped/resized. Then threw 20 of each in the ultrasonic bath (20% Simple Green Max) for 30 minutes and found that the MEN and PPU NATO primer pockets did not clean out too well. The PPU 308 pockets came out almost squeaky clean.
I’ve used the 20% Simple Green to clean small engine parts and a couple other things and they always came out spotless, not a speck of crud left after a 30 minute hot bath. So why is the crud left by NATO spec ammo so tenacious?
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The higher the pressure the higher the heat. Probably getting baked on there…harder to get off. Stainless Steel pins for the win. 
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I was thinking it might be sealant. I’ve put some really grimy stuff in the US cleaner and everything came out squeaky clean in 30 to 45 minutes.
I hear stainless is the cats meow when it comes to cleaning primer pockets.
Feel free to use mine anytime you want.
Been there. It’s the sealant. You’ll need to tumble with ss pins to get those pockets clean the first time. The good news is that once you’ve done that, your subsequent cleanings don’t have to be with pins. I have tried all methods of cleaning.Vibratory tumblers with walnut media, ultrasonic, ss pin wet tumbling. Ultrasonic is easiest and does “ok”, but not nearly as quick or as thorough as the other methods IMO (and I have a commercial u/s machine). The vibratory is cheap, efficient and has the advantage, unlike wet ss tumbling, that you can check cases frequently, add more, or pull some out with a flip of the switch. With ss wet tumbling it’s a much longer process to add some or to check. I moved away from vibratory tumbling due to the dust. My preferred method (but I am OCD for cleanliness) is to decap first, ss wet tumble, dry in clothes dryer on a cookie sheet on a sweater rack. The benefits of ss wet tumbling are 1) quieter, 2) no dust, 3) squeaky clean primer pockets 4) media lasts forever. The downsides: 1) setup and drying take time so I would only do large patches at a time (1000’s), and that requires a large tumbler, and that costs more $. 2) Although rare, pins do get stuck in cases sometimes. So, even after separating cases from pins, you must be vigilant about making 100% sure that all the pins are removed from inside the cases. Why? because you don’t want those pins running (scraping) down your barrel at 1200 fps. Do primer pockets ‘need’ to be clean? No, but again OCD. Bottom line, my choice is ss wet tumbling on a large machine, ideally with multiple small barrels, and scrutiny afterwards to remove every pin from your brass. The brass comes out looking brand new, no dust, no noise.
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