Case Lip Peening

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Case Lip Peening

Post by patchbox » Sun May 23, 2021 11:19 am

This is a new old topic and I know it has been discussed at length on previous posts; however, the reason for case lip peening with wet tumbling is not enough media. For a rotary tumbler the 5 lbs of stainless pins is totally inadequate for tumbling 50 cases of any relatively large case size. There is not enough media to provide cushioning between the brass and peening to some degree will always exist - more water, less water does change the outcome but is way less of a factor than just adding enough media. The cushioning effect of the media between the tumbling cases is the key and for that you need more media. Stainless pins are heavy so using enough in a rotary tumbler is challenging. Ceramic media is lighter than stainless volume wise but from what I’ve seen the commonly available ceramic media is pricey if buying enough to provide the cushion. I bought some ceramic porcelain polishing pins (2.5mm diameter x 8mm length) from a company called Mass Finishing. A 55 lb sack cost me $179 - this is enough to last a life time - the wear on the hard porcelain is next to nothing. So the results:
I filled a Rebel 17 (high speed motor) tumbler barrel to almost half full of ceramic pins and 50 45-70 cases. Filled with water about 1/2” above the pins. Added couple drops of dawn and tablespoon of citric acid (lemishine). Tumbled for 45-60 minutes. Brass was cleaner and more polished than I had ever seen with stainless pins and no case lip peening. I am meticulous with the case lip peening observation since I load paper patch and got tired of removing the burr so I am keenly aware of any burr on the lip. I have used the ceramic pins for the last 10 cleaning sessions on the same batch of brass and have noticed no peening on the case mouths. For me, this is the way to go for case cleaning. Rock tumbling enthusiasts use the same principal of adding enough small ceramic media to prevent chipping caused by the rocks banging into each other. Use more media to create cushioning between whatever your tumbling. Works very well for me.

John Boy
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Re: Case Lip Peening

Post by John Boy » Sun May 23, 2021 12:39 pm

Buy about 2 lbs of 3mm ceramic triangle media ... that’s all you need ... -media.htm
Wet cleaner ingredients: Strat-O-Sheen burnishing solution ... 3mm ceramic media and a 2 squirt of Dawn
Fill the tumbler with 1/2 inch of media and no more than half full of brass with solution covering the brass
Zero peening of case mouths

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Lumpy Grits
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Re: Case Lip Peening

Post by Lumpy Grits » Sun May 23, 2021 5:31 pm

Slow the tumbler RPM down, and the problem goes away.
"Hav'n you along, is like loose'n two good men"

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Re: Case Lip Peening

Post by mdeland » Tue May 25, 2021 5:55 pm

I've read of this happening for years but have never once experienced it with any brass I have. Guess I just happen to have gotten the right proportions by accident.

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