The Texas shooter was, according to early reports, armed with an “AR-15” style weapon and a handgun.
The “AR” is for Armalite — not assault rifle — the name of the company which manufactured the original AR-15. The manufacturing rights for AR-15s were eventually sold to Colt, which sold a version to the U.S. military as the M-16.
The model has since become the basis for hundreds of spinoff versions from various manufacturers. The shooting platform can be configured into infinite variations and looks, making it useful for any shooting purpose and deeply popular among enthusiasts.
The firearm may use a 5.56 NATO round or a .223 caliber, the difference being that the former is slightly longer and has a grain more powder. Other calibers are possible. Modern military models can have select fire, or a three-round burst, while civilian models do not.
The weapon is air-cooled and gas-operated. It is fed using a magazine, which can come in capacities up to 100 rounds.
Most configurations are point (person) target accurate beyond 400 meters and a trained shooter can sustain an accurate rate of fire of 45 rounds per minute.
Source: Orange County Register