LogFAQs > #982608804

Yeah the weapon "stats" don't really exist in the sequels. It's more about how the guns themselves perform. Locust has the best accuracy/stability of any SMG in the second game. Weapon choices get more varied in the third game.

As for shotguns, you can immediately get a great one from Omega. Geth Plasma Shotgun. You can also research the Eviscerator after getting the professor, also from Omega. Those are the two best for the early game.

Later you can choose to grab the Claymore which fulfills the true potential of the Vanguard. It does only have a one shot clip though, so it takes some practice getting used to. Plus if you aren't playing on Hardcore or Insanity it might not be as advantageous.