Today’s standard-issue U.S. Military rifle, the M4 carbine is essentially a modernized, compact variant of the Vietnam-era M16. Featuring a 14.5-inch barrel and generally weighing about seven pounds loaded, the M4 is a versatile, adaptable rifle that has a collapsible stock to fit a wide range of shooters. Developed in the mid-1980s, the M4 has been modernized over the years but generally shoots in both semi-automatic mode (one shot per trigger pull) and either a three-round burst mode (three shots per trigger pull) or fully automatic mode (continuous shooting with one trigger pull). The M4 features M1913 rail sections on the handguard and receiver to attach accessories and optics and is chambered in NATO standard 5.56mm.