[5][6][7] The first mass production version was the Colt AR-15 Sporter, in .223 Remington, with a 20-inch barrel, issued with 5-round magazines.

[8] On September 20, 2019, Colt announced that it would no longer produce the AR-15 for private use, due to market saturation.

[9] By May 2020, changed market conditions encouraged Colt to resume production for sales to private users.

As soon as the neck of the case clears the barrel extension, the bolt's spring-loaded ejector forces it out the ejection port in the side of the upper receiver.

As the bolt's locking lugs move past the barrel extension, the cam pin twists into a pocket milled into the upper receiver.

Upper receivers are available with barrels of different weights, lengths, calibers, and rail systems with various sights and accessories.

The early commercial SP-1 AR-15s used a pair of 0.250-inch (6.4 mm) diameter receiver push pins, identical to those found on the military rifles.

[13] The AR-15's most distinctive ergonomic feature is the carrying handle and rear sight assembly on top of the receiver.

At closer ranges (typically inside 15–20 meters), the shooter must compensate by aiming high to place shots where desired.

[17] Current versions such as AR-15A4 have a detachable carrying handle and use Picatinny rails, which allows for the use of various scopes and sighting devices.

[19] The standard AR15 muzzle device conforms to the STANAG dimensional requirements for firing 22 mm rifle grenades.

The primary distinction between civilian semi-automatic rifles and military models is select fire.

Most components are interchangeable between semi-auto and select fire rifles including magazines, sights, upper receiver, barrels and accessories.

[21] In order to prevent a civilian semi-automatic AR-15 from being readily converted for use with the select fire components, Colt changed a number of features.

Parts changed include the lower receiver, bolt carrier, hammer, trigger, disconnector, and safety/mode selector.

[23][better source needed] As designed by Colt the pins supporting the semi-auto trigger and hammer in the lower receiver are larger than those used in the military rifle to prevent interchangeability between semi-automatic and select fire components.

[26] AR-15 style rifles are available in a wide range of configurations and calibers from a large number of manufacturers.

[27][28] From April 28 to 29, 1996, Martin Bryant killed 35 and injured 23 in the Port Arthur massacre, during which he used a Colt AR-15 and a L1A1 SLR chambered in 7.62×51mm NATO.

It was the worst mass shooting in modern Australian history and resulted in the 1996 National Firearms Agreement.

This list deems the Colt AR-15, as well as the Armalite AR-15, Bushmaster XM-15, DPMS Panther, and many other AR-pattern rifles as assault weapons by name, thus illegal to own/possess in the state of California.