A GI ammo can will last almost forever. I have several that are over 30 years old and still in excellent shape. I had paint cans stored in a dry garage with solvents I them uncoated on the outside and rusted through in about 4-5 years. Paint cans are thin, if you drop loose rounds in it they may be able to penetrate the side or bottom, they bend easy and if uncoated will rust fast. Price wise for me GI cans are cheaper as they last longer, are stronger will open and close probably a million times (can't prove that have not did a actual test)and are designed to hold ammo with a strong carry handle. Paint can have to be opened with a screwdriver, church key or some other object, and for me at least the rim always bends and you lose your seal plus you have to have a item like I stated to open them. Maybe the plastic cans will last longer but like I said my preference is GI ammo cans.