What do you think causes this erosion?

[Ranch Dog]

Yeah, very puzzling. It isn't location specific as I left one in my reloading room, an entirely different building, and it did the same thing. Next step is testing the Rio Grande. I have one sitting for a couple of days. My Marlin rifles and handguns don't do it as I have noted.

[Barry in IN]

I'm betting on your dissimilar metal theory. I've seen some odd corrosion in airplanes. It might be where two different metals contacted, but the same type of contact a few inches away will be fine. It seems like a freak thing, then after looking at some more airplanes, I'd see they were the same way. Very strange.

[runfiverun]

now that's totally weird, as alox is a rust preventative.
and calcium needs water to evaporate to turn like that.
some lead alloys will have calcium in them but that shows up in the casting as troublesome.
i have seen lead bullets turn white over time even lube covered 22's.
but not just one area like that.
and not that thick.

[grandad]

certainly some action going on,i usually smear reloads with PROLIX if they are going to be in a gun for some time.
good to see you nailed that critter.
our place up close we have foxes around but biggest problem are bloody snakes, range from 1' to 7' mostly the kind that are very dangerous, they usually live in the sugar cane,before harvest the canefields are set alight to burn off excess trash, buggers come out mad as hell,i have had them get into house. have a 12g double handy for them.

[Rooster59]

Just a wild guess but are any of the circumstances new? Or did you just now for the first time look and find the corrosion? Is it corrosion/erosion or is it deposits?

Is the gun racked vertically and could oil from the barrel be collecting in the chamber running down the barrel?

I have stored my stainless 92 with ammo in the chamber on occasion but didn't experience any unusual deposits on the bullets.

[Arktikos]

Looks pretty much like what is on the sacrificial anodes on my outboard motor.

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[Ranch Dog]

Looks pretty much like what is on the sacrificial anodes on my outboard motor.

Yes, and the anode rods in my water heaters. I replace them every 18 months!

[MT Gianni]

Are you by any chance using Lee case size lubricant? I have had that show up on my brass after it got wet. When I wiped things down better it went away, and the size lube was the only common denomanator

[Ranch Dog]

Are you by any chance using Lee case size lubricant? I have had that show up on my brass after it got wet. When I wiped things down better it went away, and the size lube was the only common denomanator

I do use it, sprayed on in a rubbing alcohol solution. This erosion has stopped, haven't seen it in a month or so. Nothing has changed on my part so it is something is happening with a set of ambient environmental conditions I guess.

[runfiverun]

it had to be moisture related.
the only other thing that would cause it is the presence of aluminum.

yeah,, I have been mulling it over some for a bit now and that is really all I can come up with.