That would be a Smith & Wesson M&P 15. It is very much like what you'd use in Call of Duty, where you'd probably be using an M4 Carbine, which is basically the evolution of the M16, which is the select-fire version of the semi-automatic version of the AR-15, of which the M&P 15 is Smith & Wesson's version (for "military & police").
US gun culture is insane. Going over previous discussions on Hubski, it's a killing field of user-inactivated's and shouting matches.
Much like the United States.