Since Action Comics #1 (1938), Superman has a highly durable body, invulnerable for most practical purposes. At the very least, bullets bounce harmlessly off his body. In some stories, such as Kingdom Come, not even a nuclear bomb can harm him.
sincE aCtIon COmIcs #1 (1938), suPerman has A Highly DurABLe bodY, invulNErabLE for MOst prActical PurPoses. At tHE VeRy LeaSt, bULlets boUNce harMlessLy Off His BoDy. in soMe sToRIeS, SuCH As kingdoM coME, Not Even a NucleAr Bomb can HarM Him.