The M4 Type Carbine is a firearm manufactured by Bushmaster Firearms International, modeled on the AR-15

AR-15

The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....

 platform.
The M4 Type Carbine is effectively a reproduction of the Colt

Colt's Manufacturing Company

Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...

 M4 Carbine

M4 Carbine

The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.It is a gas-operated,...

, but is usually only semi-automatic

Semi-automatic rifle

A semi-automatic rifle is a type of rifle that fires a single bullet each time the trigger is pulled, automatically ejects the spent cartridge, chambers a fresh cartridge from its magazine, and is immediately ready to fire another shot...

 for legality within the U.S. civilian market. However, it can be ordered by military or law enforcement organizations with three-round burst

Burst mode (firearm)

In automatic firearms, burst mode or burst fire is a firing mode enabling the shooter to fire a predetermined number of rounds, usually 2 or 3 rounds and 100+ on anti-aircraft weapons, with a single pull of the trigger. This firing mode is commonly used in submachine guns, assault rifles and carbines...

 or fully automatic capability. The rifle accepts both .223 Remington

.223 Remington

The .223 Remington is a sporting cartridge with almost the same external dimensions as the 5.56×45mm NATO military cartridge. The name is commonly pronounced either two-two-three or two-twenty-three. It is loaded with a diameter, jacketed bullet, with weights ranging from , though the most common...

 and 5.56 x 45 mm NATO

5.56 x 45 mm NATO

5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...

 cartridges, and the barrel is hard chrome lined in both the bore and chamber.