What causes this? Spots on brass.

[Yankee1986]

I was given about 300 cases, mainly Hornady & WW with a few R-P.
These were the worst of the bunch, after 4hrs of dry tumbling.
Amazingly, the spots don't feel "soft" but I'm still not loading them.

 

[Mk-211]

Corrosion happens with brass, toss them as they're no good. Once it has corroded the brass that much, it's no longer good.

A weak spot could blow out and damage your firearm. Add it to your recycle bin.

Do you know how and where the brass was stored? That's probably the biggest factor in corrosion of brass.

 

[Toprudder]

I got buckets of brass from an estate of a reloader. Some of them had spots like that. Best I could tell, there were mice in those buckets that probably urinated on the brass.

 

[GeoDudeFlorida]

I was given about 300 cases, mainly Hornady & WW with a few R-P.
These were the worst of the bunch, after 4hrs of dry tumbling.
Amazingly, the spots don't feel "soft" but I'm still not loading them.

View attachment 1124970 View attachment 1124971 View attachment 1124972 View attachment 1124973 View attachment 1124974

That looks like alkyl etching. Ammonia, salts, fertilizer, something with a basic chemistry. Sweat tends to be acidic but that’s just a tendency; and, not everyone is the same. Sweat also tends to be salty so it could be from sweat or something that dripped on the cases in storage. Take a polishing wheel to one or two and see how deep the etching is. I think it’s a good call not using them.

 

[Random 8]

My guess would be contamination from something that reacts with brass. Once it starts a little bit, it seems to have a hygroscopic effect and accelerate normal atmospheric corrosion.

Mice pee, solvents, vinegar, Mountain Dew or Coke. I once had a mouse get into a bag full of .223 brass. Made a nice nest in the box it was stored in and shredded a bit of the ziploc baggie for bedding. In the course of 6 months or so, most of the brass was thoroughly corroded, some nearly eaten through. Glad it was random range brass and not my good stuff! They really raise hell with a snowmobile muffler too!

 

[Yankee1986]

Do you know how and where the brass was stored? That's probably the biggest factor in corrosion of brass.

No idea. Seems weird that only a few were affected. I'm sure they were all thrown in the gallon jug a long time ago.

 

[Riomouse911]

Had the same problems when a rat nested in my garage one winter. Piddled on, and ruined, a good bit of brass and a bunch of original pistol boxes I had on the lower garage shelf.

Pitch the damaged ones and clean the rest.

Stay safe.

 

[lightman]

I agree, some type of chemical. Mouse pee, sweat or maybe some type of Ag chemical, ect.

 

[EricBu]

Mouse piss........somebody had them out in the garage in an uncovered bucket.

 

[Tall]

I had some black powder cases that corroded like that after firing. I think they need to be tossed. Corrosion like that is permanent and hurts the structural soundness.