Yeah, people who think they know a thing or two just because they've played FPS...dumbasses. Some of the guns do feature the reality of their real-world counter parts, others are just stupid parodies. As though Infinity Ward got military advisors to help them make the game and guns "realistic" and then just decided to ignore certain things. For instance an M16A4 and an M4A1 are chambered in the exact same round, for the lay man that is they fire the exact same bullet. same size, same amount of power. And yet the M16A4 does more damage than the other for whatever reason. Same goes for the Vector and the UMP, they're both chambered in .45 ACP and yet the Vector does less damage. Go figure? Want a realistic game, play Rainbow Six Vegas 2, it's as close to how guns really work as you'll get and you won't see any F***tard shooting people while he's Dual "Wieldan". Also, a shotgun that was made ove 100 years ago should not be the best secondary weapon in the game.
P.S no one in the military or self-respecting "gun enthusiast" calls that thing the feeds ammunition in to your weapon a "clip". It's called a magazine, the clip is a device that is used to store multiple rounds of ammunition together as a unit, ready for insertion into the magazine of a repeating firearm. This speeds up the process of loading the firearm as several rounds can be loaded at once, rather than one round being loaded at a time.