The M16 is constructed of aluminium, steel and composite plastics. It is actuated by a direct impingement gas-operation with a rotating bolt, and fires 5.56mm NATO ammunition. The direct impingement operation of the firearm initially led to severe reliability problems when the rifles were not cleaned regularly. This type of operation causes hot gasses from burnt gunpowder to foul the interior of the receiver and tended to clog the action of the rifle. Switching to a different powder mostly solved this issue; however the rifle still requires frequent and thorough cleaning.
One of the main advantages of the M16 is the huge versatility of the weapon. The receiver of the weapon is made from aluminium and is split into two parts: the upper and lower. Since the upper receiver contains the barrel, gas system and bolt group, it is possible to switch barrel lengths, styles (light, heavy, fluted etc.) and even calibres relatively easily by dropping a different upper receiver onto the same lower, consisting of the trigger unit, recoil buffer, grip and buttstock.
This rifle is a M16A2, fitted with the M203 40mm grenade launcher. The M16A2 is improved over the original model with the addition of a forward assist (to push the bolt into battery in the event of a jammed cartridge), tighter barrel rifling, a stronger barrel, improved adjustable sights, a modified flash suppressor, more comfortable handgrips, improved buttstock and a spent case deflector on the upper receiver. Most noticeably, the fully automatic setting was replaced with a three-round burst setting to conserve ammunition.
The M16A2 has a rate of fire of 800rpm and is effective out to ranges of 550 metres. It feeds from a 30 round box magazine and weighs 3.77 kilograms empty. The M203 grenade launcher fires a variety of 40mm grenades at ranges of up to 350 metres (against area targets) and weighs 1.36 kilograms unloaded.