XM-177

The XM177 (commonly called the Colt Commando or part of the CAR-15 family) is a short-barreled variant of the M16 rifle platform, developed by Colt in the mid-1960s during the Vietnam War. It was designed to meet the U.S. military's need for a compact, lightweight firearm suitable for jungle warfare, special operations, close-quarters fighting, and use by helicopter crews or reconnaissance teams—where the full-length M16's 20-inch barrel was cumbersome and prone to snagging on vegetation.

The XM177 traces its roots to the AR-15/M16 family. Colt acquired the AR-15 design from ArmaLite in 1959 and marketed a family of weapons under the CAR-15 name (Colt Automatic Rifle-15) as a modular system based on the M16 receiver. Early short-barreled experiments included prototypes tested in Vietnam as early as 1965 under projects like ENSURE and Agile, but these had issues like excessive muzzle flash, noise, and reliability problems from the ultra-short barrels.

In response, Colt refined the design. The key breakthrough came with the addition of a large moderator (a flash/sound suppressor-like device, often 3.5–4.5 inches long) to reduce flash and blast while maintaining backpressure for reliable cycling. This made the weapon far more practical than earlier short ARs or traditional submachine guns.

Key Variants and Timeline

1966: The U.S. Army ordered 2,815 units of Colt's Model 609 (10-inch barrel, forward assist) on June 28. Designated XM177E1 (Submachine Gun, 5.56 mm) in Army service. Deliveries completed by March 1967.
- Most shipped with 20-round magazines due to early reliability issues with 30-rounders (only a few went to the 5th Special Forces Group).
- Air Force version (no forward assist): Colt Model 610, designated GAU-5/A.
1967: Field feedback highlighted issues with the 10-inch barrel (excessive flash/noise, reduced velocity/accuracy, and extraction problems from uncoated chambers prone to corrosion).
- Colt responded by lengthening the barrel to 11.5 inches, adding a chrome-plated chamber, reinforced round handguards, a simpler telescoping stock, and a grenade-launching collar on the moderator (for the XM148 grenade launcher).
- New Colt models: 629 (with forward assist) and 649 (without).
- Army designated these XM177E2; about 510 were ordered in April specifically for MACV-SOG (Military Assistance Command, Vietnam – Studies and Observations Group). Deliveries finished by September 1967.
- Air Force equivalent: GAU-5A/A (no forward assist).

The XM177E2 became the most iconic and widely praised version, offering better muzzle velocity (+~229 ft/s with M193 ammo), reduced blast, improved reliability, and compatibility with grenade launchers.

Service in Vietnam

The XM177 series was issued almost exclusively to elite units:

U.S. Army Special Forces (Green Berets)
MACV-SOG reconnaissance teams (nearly every SOG team carried XM177E2s)
Long Range Reconnaissance Patrols (LRRPs)
Navy SEALs (received some E2s)
U.S. Army helicopter crews and Air Force security personnel (as survival/PDW weapons)

Its compact size (about 29–33 inches overall, depending on stock position), light weight (~5.3–5.8 lbs), and 5.56mm firepower made it ideal for jungle patrols, ambushes, and vehicle/boat operations—far superior to submachine guns like the M3 Grease Gun in range and penetration.

Post-Vietnam and Legacy

Production ended around 1970 as U.S. involvement wound down and Vietnamization shifted focus. Many remained in use into the early 1970s, with troops scavenging parts from damaged rifles.

After the war:

Some captured or left-behind XM177s were refurbished by Vietnam (e.g., removing moderators and adding birdcage flash hiders to create the M18 carbine).
The design directly influenced later carbines, leading to the M4 (adopted in the 1990s with a 14.5-inch barrel).
The XM177/CAR-15 Commando remains legendary among collectors and enthusiasts for its Vietnam-era role and as a precursor to modern short-barreled AR platforms.

Parts List

Lower Parts:

Lower Receiver: Colt Gray XM177/E2

Trigger: Colt Mil-Spec

Stock: CAR-15 Aluminum Stock with Vinyl Acitate

Grip: Colt A1

Trigger Guard: Colt Gray Mil-Spec

Buffer Tube: Colt Gray 2 Position

Rear Sling Mount: Built into stock

Upper Parts

Upper Receiver: Colt A1 Gray with Forward Assist

Barrel: 11.5" with Moderator