Benneli XM1014 -- $3000

The XM1014, or auto-shotty as it is commonly called in game, is just what it says it is, a fully automatic shotgun. This gun is capable of emptying its 7 12-guage rounds in about 3 seconds. While not as powerful as the M3, the speed of this gun makes up for it. Unfortunately, you will use more ammo with this gun, and will be more likely to run out. It might take 1-2 shots to kill with the M3, so you can get at least 4 kills before reloading, while with this gun you may end up wasting 4 shots per guy, and thus only maybe get 2 kills per reload. It also costs a lot more and has the same 32 rounds in reserve as the M3, so it's really preference which one you should use, if you like shotguns.