This lower was in a trajic accident and can only use a KNS takedown pin from now on.
Wikipedia says:
Colt CommandoM4 Commando
Type Carbine
Place of origin United States
Specifications
Weight Empty: 5.38 lb (2.44 kg)
Length Buttstock extended: 30 in (760 mm)
Buttstock retracted: 26.8 in (680 mm)
Barrel length 11.5 in (290 mm)
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Muzzle velocity 2,611 ft/s (796 m/s)
Though Colt has focused its attention on carbines with 14.5-inch barrels and rifles with 20-inch barrels, Colt continues to make carbines with 11.5-inch barrels, which it calls Commandos. Commandos are assembled from whatever spare parts are available, so Model
733 Commandos can have A1-style upper receivers, A1-style upper receivers with case deflectors, or A2-style upper receivers, and M16A1-profile 1:7 or M16A2-profile 1:7 barrels. Depending on the specific models, current Commandos may have three-position fire control groups (safe/semi-automatic/three-round burst), or four-position having both full-automatic and burst. The Model 933 has a "flattop" receiver, with a removable carrying handle and a MIL-STD-1913 Picatinny rail. Though originally called the M16A2 Commando, Colt now markets it as the M4 Commando.
Some American special operation forces, such as Army Special Operation Groups, use the M4 Commando in a limited capacity. Marine Force Recon personnel sometimes use M4 Commandos in place of their US M9 pistols.[9]
The Colt Commando's 11.5-inch barrel creates a substantially lower muzzle velocity and greater muzzle flash, in comparison to longer M16 carbines and rifles. The lower muzzle velocity may reduce wounding effects.[10] In 2005, Colt came out with a semi auto only version of the 733. The designation of this rifle is the 6933.
Recently, the Mk 18 Mod 0 with a 10.3-inch barrel has taken the role of ultracompact carbine with the U.S. Navy SEALs