The M-500, is a pump-action shotgun featured in Tom Clancy's Splinter Cell: Conviction. It is the only shotgun available in the standard edition of the game, and can be acquired early in the single player game in Kobin's Mansion. And later on almost all single player missions you will find enemies carring M500 shotgun. 

Although it is a pump-action weapon, the M-500 can be fired very rapidly, and is usually lethal with just one shot at close range. Its power decreases dramatically at intermediate ranges, however, and being unsuppressed, it is very conspicuous when fired. It can be upgraded with a reflex sight, a laser sight, and match-grade ammunition, though the latter two have little practical value given the shotgun's inherent inaccuracy.