Not my post but a copy . This is one of the ways we used to test it
THE BRITE NAIL TEST
1. Take a suspect round, pull the bullet and dump out the powder. Best to also take a known corrosive round as well for comparison.
2. Take a few brite (i.e. non-galvanized) steel nails with a head size just large enough to fit into the case mouth. Degrease the nails in acetone or other and roughen them slightly with sandpaper. Drive the nails into a block of wood.
3. Slip the empty cartridge cases over the nail heads, and taking appropriate safely precautions (shielding, eye protection, gloves, etc) pop the primers with a punch and hammer.
4. Leave the cases undisturbed on the nails for 24 hours in a warm place (I usually leave them on top of the water heater) and then examine the nails.
If the nail looks black and smokey, then the ammo is noncorrosive. If the nail has red flecks, then the ammo is corrosive. It will be obvious - but doing a known corrosive ammo as a control is helpful.