The McDonnell Douglas AIWS (short for Advanced Infantry Weapon System) was a prototype assault rifle entered in Phase I of the Advanced Combat Rifle program.
The AIWS was created by Hughes Helicopter Systems, later known as McDonnell Douglas. The weapon was tested with a variety of different ammunition types, all of which proved fairly unreliable, as the cartridge used required more propellant than the average cartridge. The AIWS was ultimately withdrawn early from testing, with McDonnell Douglas citing technical issues.
The AIWS used lockless "chiclet" rounds that were first used in older prototypes made by Hughes. A saboted flechette was positioned in the center of the cartridge with the powder compartments on either side, with the "lockless" chamber closed off at the breech end with a slot at the top and bottom of the barrel. Ammunition is fed into the chamber from the magazine located on the left side of the weapon and a sliding pressure sleeve closes off the barrel’s openings. Once the round is fired, this sleeve retracts and the spent casing is pushed out of the ejection port by the next round feeding from the magazine.
The AIWS uses lockless "chiclet" rounds, which were first used in older prototypes tested by Hughes Helicopters. The rounds are nicknamed chiclets due to the flat, box-like profile of the casings resembling the popular candy-coated chewing gum. The original loads for the rounds were duplex or triplex loads of normal bullets, but these caused excessive recoil; the loads were later changed to fléchettes of either 11mm or 8.6mm calibers.