"The three types of weapons used by the man accused of killing 12 people in a Colorado movie theater — a semiautomatic variation of the military’s M-16 rifle, a pump-action 12-gauge shotgun and at least one .40-caliber semiautomatic pistol — are among the most popular guns available in the multibillion-dollar American firearms market...It appears, the police say, that James E. Holmes, the man accused in the Aurora shootings, used all three types of weapons inside the theater as well, first firing the shotgun, then using the semiautomatic rifle until its 100-round barrel magazine jammed, and finishing off with a pistol. ...much of the public and political attention has been focused on the potential deadliness of the semiautomatic rifle, which law enforcement officials identified as a Smith & Wesson M&P15. The rifle belongs to a class of weapons broadly known as AR-15s, after the original civilian version of the rifle.... The M&P15 also comes in a variety of models that fire different sizes of ammunition, from .22-caliber to .30-caliber rounds. The rifle used in Aurora fired .223-caliber ammunition, law enforcement officials said. Those rounds — similar to the ammunition used in American M-16 and M-4 rifles — are smaller than the rounds fired by Afghan insurgents wielding Kalashnikov rifles, but pack far more power than .22-caliber rounds, even though they are only a hair’s-width larger in circumference."