M16A1

Here are some images of Trumpeter's 1/3 scale AR15/Mi6/M4 Family M16A1 Rifle.

From Wikipedia"

The M16 (more formally Rifle, Caliber 5.56 mm, M16) is the United States military designation for the AR-15 rifle. Colt purchased the rights to the AR-15 from ArmaLite and currently uses that designation only for semi-automatic versions of the rifle. The M16 rifle fires the 5.56x45mm cartridge and can produce massive wounding effects when the bullet impacts at high velocity and yaws in tissue leading to fragmentation and rapid transfer of energy.

The M16 entered United States Army service and was deployed for jungle warfare operations in South Vietnam in 1963, becoming the standard U.S. rifle of the Vietnam War by 1969, replacing the M14 rifle in that role. The U.S. Army retained the M14 in CONUS, Europe, and South Korea until 1970. Since the Vietnam War, the M16 rifle family has been the primary infantry rifle of the U.S. military. With its variants (M16A1, M16A2, M16A3, and M16A4), it has been used by almost a hundred countries. Total worldwide production of M16-style weapons since the design's inception has been approximately 8 million, making it the most produced firearm in its caliber. The M16 is being phased out in the United States Army and is being replaced by the M4 carbine series as of 2010.

XM16E1 and M16A1 (Colt Model 603)

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967. To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued while barrels with chrome-plated chambers and later fully-lined bores were introduced.

With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such a way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject until corrected. The M16A1 remains in service in limited numbers in the United States but is still standard issue in many world armies.