Colt GAU-5/A/A Carbine Replica Honors Spec Op Raiders of Son Tây Prison

The rifle seen here is a Colt replica of the carbine used during the historically significant Son Tây Raid that occurred on November 21, 1970. The raid would go on to serve as the model of how U.S. Special Operations elements would plan and execute sensitive missions for decades into the future. The heavy emphasis the raiders placed on pre-mission planning and mission rehearsals would also become a hallmark of all of Special Operations’ missions to present day. The rifle used during the raid would also serve as the basis for what U.S. Special Operation units still issue. This replica is a tribute to one of the “founding fathers” of the M4 carbine.

U.S. Special Forces soldiers in Vietnam began using the XM177, XM177E1 and XM177E2 as early as 1966. The XM177 and XM177E1 had 10-inch barrels with separate sound moderators attached. The moderator helped eliminate muzzle flash and blast, and made the short-barreled carbine sound more like the 20-inch barreled standard-issue rifle. The long cylindrical flash hider on Colt’s replica carbine is made to look like the moderator of old. (Unfortunately, it cannot serve the same function or else it would be classified as a restricted item.) What’s on this rifle is simply a flash hider, but it is stretched and styled to mimic the original moderator.

The XM177 was Colt’s name for the carbine the U.S Air Force referred to as the GAU-5/A. “GAU” stands for“Gun, Automatic, Unit (as opposed to a gun built from parts), and the only difference between the XM177 and XM177E1 is the XM177’s lack of a forward assist on the upper receiver. The Air Force was adamant about maintaining the original configuration of the M16 and the absence of the forward assist from their rifles and carbines. They felt this way because Eugene Stoner never designed the rifle to have one. The addition of the forward assist occurred after the infamous “one-time buy” of more than 20,000 M16s in 1962. Secretary of Defense Robert McNamara wanted the rifle to be used across all branches of service, so all branches had to agree on the configuration. The Army wanted the soldier to be able to manually close the bolt in case the rifle became dirty and wouldn’t close on its own. The U.S. Navy and the Marine Corps equivocated like bureaucracies often do. The Air Force took their cue from Eugene Stoner who said, “I was always afraid of a bolt-closure device myself because when you get a cartridge that won’t seat in a rifle and you deliberately drive it in [to the chamber], usually you are buying yourself more trouble.” Any time the Air Force purchased the small amounts of XM177s, they always purchased them without the forward assist. That’s why this replica GAU-5/A/A has no forward assist; no GAU-5 carbine ever did. However, the Army eventually won the battle with the forward assist becoming a standard feature on the M16A1, which was adopted in 1967.

Inspection of the lower receiver markings on this carbine show “GAU-5/A/A”, which is the nomenclature the Air Force used on their version of the XM177E2. The changes made on the XM177E1 to yield the XM177E2 were mostly internal, but the easiest one to recognize is the raised protective “fence” around the magazine release. The XM177E2 also had an 111/2-inch barrel with a 1:12-inch twist rate instead of the shorter 10-inch barrel with 1:14-inch twist found on the XM177, XM177E1 and GAU-5/A.

Colt’s efforts to make this GAU-5/A/A as period-correct as possible wouldn’t have been possible without Curtis Debord of U.S. Ordnance, with whom they teamed for this project. One detail that would have been easy to overlook is the use of a non-reinforced lower receiver, which is what Colt would have built these guns with at the time. The lower receiver had some additional mass added in the area behind the take-down pin and the lower receiver extension (i.e., buffer tube) with the adoption of the M16A2. Just about every lower receiver made today has the improved lower receiver. Another bottom-half feature that is correct is the presence of overtravel stops above the “SAFE” and “AUTO” markings. Kudos to Colt for putting “AUTO” on this receiver even though it’s not possible for this carbine to fire automatically, per the law. Finally, the lower receiver even has the white-paint acceptance stamp of the Ordnance Corps that was in use at the time original carbines entered service.

The upper receiver stayed true also by retaining the angled delta ring that holds the small-diameter handguards in place. Both the delta ring and handguards are correct for the original carbines. Photos from the Son Tây raid show GAU-5 rifles with both straight and tapered delta rings. (Technically, either version would be correct.) Colt also used the small-diameter handguards with a single internal heat shield in keeping with the design issued at that time.

The barrel with the permanently ­affixed flash hider is the least-correct feature on this retro carbine, but that’s because today’s NFA laws require it. The barrel has the historically ­accurate 111/2-inch length with 1:12-inch twist rate. The flash hider is 43/4 inches long, making this retro carbine slightly longer than the GAU-5 issued to the Son Tây raiders. It does ensure the barrel, overall, exceeds the 16-inch mandated length to avoid an SBR tax

The collapsible buttstock is another area where Colt’s historical efforts show. The GAU-5/A/A has a two-position lower receiver extension that places the buttstock either close to the lower receiver or extended to its full length of pull. The buttstock is made from aluminum and coated with vinyl-acetate, again, just like the originals.

Downrange accuracy from this carbine was as expected for using period iron sights and a non-free-floating handguard. The best five-shot group at 100 yards measured 1.95 inches. Groups would likely improve with a magnified optic, but the average across three loads hovered near 21/2 inches. It was no surprise that 77-grain ammunition would not group at all, and we do not recommend this grain weight for use in this rifle due to the barrel’s slow 1:12-inch twist rate.

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The amount of detail and effort applied to building each of these GAU-5/A/A carbines makes them expensive. Each retail for $2,600. These carbines are probably not going to be a hot item for the casual AR-shooter, but they will have strong appeal for many, including veterans. Anyone that wants a working sample of a rifle inspired by the GAU-5/A/A used to help launch U.S. Special Operations would be interested in this tribute. 

COLT GAU-5/A/A RETRO CARBINE SPECS

Guns & Ammo photo
• TYPE: Direct impingement, semiautomatic
• CARTRIDGE: 5.56 NATO
• CAPACITY: 20 rds.
• BARREL: 16.1 in.; 1:12-in. twist
• OVERALL LENGTH: 32 in. (collapsed); 35.5 in. (extended)
• WEIGHT: 6 lbs., 8 oz.
• STOCK: Two-position collapsible; die cast, vinyl acetate-coated aluminum
• LENGTH OF PULL: 10 in. (collapsed), 13.5 in. (extended)
• GRIP: M16A1-type, glass-reinforced polymer
• FINISH: Anodized (aluminum)
• SIGHTS: Aperture, windage adj. (rear); post, elevation adj. (front)
• SAFETY: Two-position selector
• MSRP: $2,599
• MANUFACTURER: Colt, 800-962-2658, colt.com