The M4 carbine is a gas-operated, magazine-fed, 5.56x45mm NATO carbine designed in the United States in the '80s. It is a shortened version of the M16A2 assault rifle. Colt has produced many M4 civilian variations and lines over the years, each of which is distinguished by a four-digit number that comes after a specific prefix (LE, CR, etc.). The Colt M4 Carbine, officially known as the Colt M4 Carbine Model 6921, features a 14.5-inch chrome-lined barrel, equipped with a pinned flash suppressor to meet legal length requirements and reduce muzzle flash. The M4 Carbine is designed with a collapsible stock, allowing for adjustable length of pull to accommodate various shooting positions and body sizes. Its flat-top upper receiver includes a removable carry handle with integrated iron sights, which can be replaced or supplemented with various optics via the Picatinny rail. The rifle operates in semi-automatic mode or full-auto/burst configurations, depending on the model, making it suitable for both tactical and combat scenarios. With the introduction of the Colt LE (Law Enforcement) M4 Carbine semi-auto rifle, the battle-tested M4 platform takes a tactical turn. The Colt LE6920 is a series of 5.56x45mm NATO-chambered semi-automatic AR-15 M4 Carbine versions. It is designed for civilian use, whereas the M4 is a select fire weapon, and the 6920 has a 16-inch barrel to comply with US gun laws, while the M4 has a 14.5-inch barrel. M4 civilian copies often feature 16-inch barrels (or regular 14.5-inch M4 barrels with flash suppressors permanently attached, for a total length of 16 inches) and are semi-automatic, just to fit the legal definition of a rifle under the US Gun Control Act. The Colt OEM Series provides customers and dealers with an unconditional alternative for customizing rifles based on the tried-and-true Colt M4 Platform. In OEM1 and OEM2 versions, handguards, buttstocks, trigger guards, magazines, and rear sights have been completely removed.