This is the NEWEST V2 from JG with reinforced metal bushings/internals, M120 spring, and JG's newest ultra high-torque motor.

Jing Gong SR25K Airsoft Electric AEG Rifle (FB6651)
-- Full Metal Construction
-- 416 Type Battery Fixed Stock
-- Fully/Semi Automatic Shooting Mode
-- Package include Foregrip, 9.6V 1100mAh Battery & Charger

The M16 was an initial version first adopted in 1964 by the United States Air Force (USAF). The U.S. Army began to field the XM16E1 en masse in 1965 with most going to Vietnam. The US Marine Corps also adopted the system during this period. The XM16E1 was standardized as the M16A1 in 1967. This version remained the primary infantry rifle of the United States military from 1967 until the 1980s, when it was supplemented by the M16A2. During the early 1980s a roughly standardized load for this ammunition was adopted throughout NATO (see: 5.56 mm NATO).

The M16A3 is a fully-automatic variant of the M16A2, issued primarily within the United States Navy. The M16A2, in turn, is currently being supplemented by the M16A4, which incorporates the flattop receiver unit developed for the M4 Carbine, and Picatinny rail System. M16A2 are still in stock with the U.S. Army and Marine Corps, but are used primarily by reserve and National Guard units as well as by the U.S. Air Force.

(Courtesy of Wikipedia)