I found an interesting article on the origin of the "carbine" M16 that eventually evolved into the Colt M4, LE6920. Most of us already know this story by heart, but it's still an interesting read, like revisiting a favorite book:
https://nationalinterest.org/blog/bu...do-rifle-39617
U.S. Army Special Forces troops were on the ground advising South Vietnamese Army units, and in that capacity, the green berets often carried older weapons such as the M-2 carbine. The M-2, dated to the Korean War, was more suited to the size and stature of Vietnamese troops than the M-14 and U.S. advisors carried them to increase commonality with the troops they advised (and sometimes led.) Although a useful weapon, the older .30-caliber cartridge lacked the power of the new, modern 5.56 cartridge.Colt’s solution to the short rifle problem was the CAR-15. Derived from the Colt Model 607 carbine, the CAR-15 featured a sliding buttstock that reduced overall length and the barrel was shortened from the 20 inches of the M16 to 10 inches.The Pentagon signed a contract in June 1966 with Colt for 2,815 Colt “Commando” rifles, although officially it was known as a “Submachine Gun, 5.56-mm, CAR-15”. Colt completed the deliveries within six months. The first rifles sent to the military were unmodified Colt 607s, designated XM177 in Air Force service and XM177E1 in Army service. Right away soldiers noticed some issues with the new weapon. One major problem was that the drastic shortening of the barrel led to a large, bright fireball at the muzzle and very loud gunshot report—clearly, the flash hider designed for the rifle was not up to the task. Soldiers also noted a problem with accuracy and thought the buttstock too complicated.
Within weeks Colt was back to the drawing board and the result was the new Colt 629 Commando. The 629 featured a slightly longer barrel, at 11.5 inches, and a newly redesigned flash hider. A chrome-plated chamber helped prevent gunpowder residue from accumulating in the upper receiver, leading to stoppages. The result was what the company believed was the best compromise between a compact weapon and one that generated an obnoxious amount of noise and light on the battlefield. The 629 was rebranded the XM177E2 and the Army placed an order for 510 of the E2 rifles in early 1967; the rifles to go to the U.S. Army’s Studies and Observation Group (SOG), Vietnam. Despite the bookish name, SOG was a cover for U.S. Army special forces reconnaissance teams operating in South Vietnam, North Vietnam, Cambodia and, later, Laos. Operating deep within enemy territory for days at a time, green berets and the local troops that fleshed out their recon teams liked the CAR-15 for its compactness and firepower.Another special forces unit that used the CAR-15 in action were U.S. Navy SEAL teams. SEALs originally carried the Colt 607 but transitioned to the XM177E2 when available. Both SEALs and U.S. Army Special Forces continued to use the XM177 well into the 1970s, working around the lack of new production by cannibalizing some rifles to provide spare parts for others.My first AR was a CAR-15 clone with pencil barrel, A1 sights, and skinny handguards. My modern favorite rifle is the Colt LE6720: basically the same thing but with the 1913 rail instead of the fixed carry handle. Still, I keep a bone stock Colt M4 with the carry handle, and fat foregrips. Unlike the LE6720, which says "AR15A2" on the side, my genuine Colt M4 LE6920 says "M4 Carbine" on the side. It's a piece of history, and as close as a civilian can legally get to a real military M4 right off the shelf. I was looking at my M4 sitting on the rack last night. It looked rather lonely and unloved. It's got a few scratches from use, but it's the one that usually stays at home while I fire my 6720 or 6520 (fixed carry handle pencil barrel) carbines. I aim to change that. Next range trip the "M4 Carbine" is the one that gets shot.The concept of a shorty M16 went dormant into the 1980s, but in the 1990s the U.S. Army officially adopted the M4 carbine . Although not as short as the Colt Commando, as an offshoot of the original weapon separated by more than twenty years of research and development, the M4 is a more reliable and generally refined design. Today the M4 is the standard weapon assigned to U.S. Army and Marine Corps infantrymen worldwide.
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