TSD Sports Competition M4A1 AEG Specs: 

• FPS: 330-360 w/ 0.20g
• GenII Gearbox: Metal Reinforced, M110 Spring
• Bushing & Gears: Steel
• Fire Modes: Semi-auto, Full-auto, Safe
• Hop-up: Metal / Adjustable
• Receiver: ABS Plastic
• Battery & charger not included. (Use ERBAT1, ERCHARGERS or ERUSC01)
• Outer Barrel: Aluminum
• TM compatible
• Only one gun. The photos above show each side of the same item.

About the M4:

The M4 and variants fire 5.56 x 45 mm NATO ammunition and are gas-operated, air-cooled, magazine-fed, selective fire firearms with a telescoping stock. Original M4 models had a 4-position telescoping stock, but newer models are now equipped with a redesigned 6-position telescoping stock. A fixed stock can also be fitted, but this is not a common practice in the U.S. military.

As with many carbines, the M4 is handy and more convenient to carry than a full-length rifle. While this makes it a candidate for non-infantry troops (vehicle crews, clerks and staff officers), it also makes it ideal for close quarters combat (CQC), and airborne and special operations. It has been adopted by United States Special Operations Command (USSOCOM) and is the preferred weapon of the U.S. Army Special Forces. Malaysia purchased M4 Carbine service rifles to replace the Steyr AUG service rifles in its armed forces in 2006.

The M4 was developed and produced for the United States government by Colt Firearms, which has an exclusive contract to produce the M4 family of weapons through 2009; however, a number of other manufacturers offer M4-like firearms. The M4, along with the M16A4, has mostly replaced M16 and M16A2 firearms; the U.S. Air Force, for example, plans to transition completely to the M4 Carbine. The M4 has also replaced the M3A1 submachine gun that remained in service (mostly with tank crews). The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family, though unlike them it is not intended to fire the earlier M193/6 ball ammunition. Source: Wikipedia.org