I just bought some surplus ammo from Graf and Sons and some of it has some heavy tarnish on it, at least that's what their website claims. Whats the difference between ammo that is tarnished and ammo with corrosion. How can I tell the difference.
Tarnish is just discoloring/ dullness sometimes referred to as a patina. Corrosion will be more like crud growing on the metal, but it is chewing it away, like when you see white funk on your car battery terminals, except this will be green. Welcome aboard!
Corrosive ammo can also mean the primer has mercury, which is corrosive to the inside of your barrel. It is only of concern if not cleaned properly with a quality bore cleaner, any GI bore cleaner is sufficient to remove the corrosive primer deposits.
That is why many shooters of inexpensive corrosive surplus ammo buy GI bore cleaner.
As stated "Tarnish" is just a dark discoloration
While Corroded is like a Green Crude growing on the Brass
Several years back I had Gotten some Greek HXP 30-06 (Non Corrosive Ammo" and many of the cases were corroded, green crude growing (for lack of a better description) on them. To straighten them out I took 600- 800 grit emery cloth and then 0000 steel wool to them and they were and shot just fine .
The green stuff you see is actually the brass being eaten away. In light cases it is just surface corrosion/tarnish and can be removed by hand polishing as shown above. Given enough time or added moisture, a crater will actually form in the brass. It can be seen under magnification, or felt with your fingernail. The case wall thickness is decreased in this crater. The brass metal also becomes more brittle in this spot. Again, given enough time it will eat a hole thru the case wall. Firing severly corroded ammo could blow a hole in the case wall causing damage to the weapon/shooter. If your ammo does not clean up easily using a light polishing, serious thought must be given to just pulling the bullets, and scraping the severly corroded brass pieces. dozier
Corrosion is a process by which metal atoms with a charge are transported from one place on a surface to another with lower electromotive force. Essentially there is a wet cell operating there, metal atoms being plated out of where the pit is and deposited elsewhere. When deposited elsewhere, the pile of atoms has incredible surface area, and oxidizes ("rusts") easily and quickly, giving your the green on brass.
You can have corrosion without oxidation. You can have oxidation without corrosion.
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