Mainly that it is likely corrosive...which I guess just means I need to clean the gun better after shooting.
What is your experiance with surplus?
They shoot great. No problems producing good groups, only shot at 50 yards due to range limitations. I use hoppes No. 9 and clean right after shooting. I have a Otis Cleaning System, so cleaning is pretty easy. Hoppes will neutralize the corrosive salts. So far no problems with rusty on my Mosin.