Styrofoam Shell Trays Discoloring Brass ?

[billt]

Has anyone else noticed this? I reloaded a bunch of .223 / 5.56 MM a while back, and of the few boxes of the stuff I have left, I noticed the part of the cartridge that sticks out of the tray was tarnished and discolored. It's nothing to be concerned about, I just wonder why this is happening? The ammo was stored in Midway paper "CB" white cardboard ammo boxes with Styrofoam trays that hold the cartridges. I opened a box of Winchester White Box 9 MM factory ammo that I've had lying around for a while, and it had the same discoloration on the cases where they stood above the Styrofoam tray.

I'm thinking the Styrofoam itself gives off some kind of gas that discolors the brass over time, but I don't know. The part of the cartridge that is inside the tray itself remains shiny. You would think that would discolor more being in closer contact with the Styrofoam, but that is not the case.

[Timothy]

The exposed brass has more oxygen around it which is causing the brass to tarnish I'd expect.  The part of the cartridge that's is inserted into the polystyrene is more protected in a smaller area.

[billt]

I bought a bunch of Greek .30-06 ammo from the CMP a couple of years ago that was packed in flimsy cardboard boxes inside sealed "Spam" cans. They said there was discoloration on some of the rounds because of the glue that was used on the cardboard boxes. Mine was pretty good, and I didn't have much in the way of discolored rounds. Again, I'm thinking it was associated with some type of gas or vapor given off by the glue. I repackaged the can I opened in the same type of cardboard box with a Styrofoam tray, but so far no discoloration has occured.

[tombogan03884]

It's because "Styrofoam is made with Di hydrogen Monoxide.

[Timothy]

Polystyrene does off gas but it should subside over time as the material stabilizes.  Glues have all kinds of solvents and stuff but once they've evaporated, they shouldn't be an issue.  Packaging adhesives are generally not solvent based though.

[Sponsor]

[Timothy]

BTW..."Styrofoam" is an extruded polystyrene and not used in packaging.  What they use for this type of packaging is "Expanded" polystyrene.  They're probably closely related chemically.

[MikeBjerum]

It's because "Styrofoam is made with Di hydrogen Monoxide.

Smart Ass 

[jaybet]

Tarnish and rust are also called "oxidation". Eliminate oxygen, you greatly reduce tarnish.

[Solus]

It's because "Styrofoam is made with Di hydrogen Monoxide.

I think there is a lot of hydroxyl acid in there too 

[tombogan03884]

For a serious reply I would suggest, if it bothers you, rather than just curiosity, that you switch to those plastic holders like other manufacturers use that hold 10 rounds. (I think Winchester uses them )
I'm not sure where you could find them in bulk, but check Midway, and Brownell's, if they don't have them check plastic manufacturers like MKM that supply ammo boxes and reloading blocks.