Rock salt shells do no DMG, but always possess the STN modifier (inflicts Stunned).
Using rock salt shells limits the weapon to Close Range.
Rock salt rounds are a type of less-lethal buckshot used traditionally to deter trespassers in agricultural estates. They consist of salt crystals which do not retain much energy and will not penetrate much into the human skin. However, they are more lethal than rubber alternatives, so caution should be a given.