Gas Check Tarnish

Recently I had to dig out an old box of .357Mag Gas Checked Bullets.

Some Lyman #358156, these were cast from 35 - 40yrs ago. And Checked with a combination of old Lyman brass slip on and Hornady copper crimp on.
The brass gas checks were as bright, shiny and clean as the day they came out of the box. The copper checks were heavily tarnished and discolored.

Can't figure out why the copper were tarnished and the brass were not.

They were stored in a cardboard box, just dumped in. Bottom, back shelf. Untouched for 30yrs.

Different Brass and Copper alloys tarnish at different rates.

I've got a bunch of crimp ons from the 80's, and they're a little tarnished.
I ran some of them in the polisher so they'd look pretty, and they still work.

Some cardboards outgas as they age
This is most likely what caused the changes

http://lenzarts.com/framing/conservation_terms.html

Brass is a combination of Copper and Zinc....Zinc is an "anti-corrosive" additive as well as a hardner. Its in small quantities, but its enough to keep the tarnish rate much lower that pure copper.

redhawk

My old copper checks have all turned a dark brown ...it's just the nature of a metal high in copper .
Look at old copper roofing or roof flashing...the good stuff will be a dark brown .

My checks were stored in the small round tin can they came in (can't remember if Lyman or Hornady)
and they still turned brown ... it doesn't hurt them , go ahead and use them .
Gary

Copper roofing turns GREEN. Especially if it is acid washed.

It's possible someone in the past annealed the copper gas checks. I don't as a rule anneal gas checks but I had some troublesome .22 checks that I annealed and they turned very dark.

If you use them, when you shoot them you'll probably never see them again. And I'd bet they would work just as well as a brand new one.

Well, it might be more chemically correct to suggest that zinc is a "sacrificial metal" . It gives up it's ions more readily than other elements. It's the reason zinc "anodes" are used in marine environments, especially on aluminum engine parts exposed to water.

So, copper will indeed oxidize faster than brass. Cartridge brass, btw, is also called 70-30 cartridge brass. 70% copper and 30% zinc.

Quote:

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Originally Posted by redhawk0

Brass is a combination of Copper and Zinc....Zinc is an "anti-corrosive" additive as well as a hardner. Its in small quantities, but its enough to keep the tarnish rate much lower that pure copper.

redhawk

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