The discussion focuses on the US Army’s Advanced Combat Rifle (ACR) program, not the Bushmaster ACR carbine. The ACR program, active from 1986 to 1990, followed earlier efforts like the SPIW program and preceded the Objective Combat Weapon (OCIW) work. At the time, the standard service rifles were the M16A1 and the newly adopted M16A2 in 5.56×45mm. Testing had shown that under stress, soldiers achieved less than a 10 percent hit rate at roughly 220 meters. The ACR program’s primary goal was to at least double that hit probability through new rifle and ammunition concepts. The effort ultimately cost around $300 million, raising the question of what practical benefits, if any, emerged from the investment and experimentation.
The ACR program unfolded in three phases. In the first phase, the Army issued a solicitation and initially invited six participants. McDonnell and Ares were disqualified early for not having sufficiently mature systems but later won appeals to reenter. However, they were unable to deliver complete test samples before the program ended, so their designs were not fully evaluated. The remaining four active competitors were Heckler & Koch (HK), Colt, AAI (originally Aerospace Armaments Inc.), and Steyr. These four companies submitted rifles that were actually tested as potential replacements for the M16 series. The video focuses on the AAI, Steyr, and HK G11 entries, examining how each attempted to improve hit probability through unconventional mechanisms and ammunition types.
AAI’s submission was a flechette-firing rifle derived from earlier SPIW concepts. Instead of a conventional bullet, it launched a small dart-like projectile, about 1.6 mm in diameter, sometimes finned for stabilization. AAI experimented with multiple-dart loads but ultimately submitted a single-flechette configuration. The design used a standard 5.56×45mm brass case to house the flechette and propellant, which created a serious safety concern: the chamber and gas system could physically accept normal 5.56 ammunition, but firing it would be extremely dangerous. AAI tried earlier interchangeable concepts and abandoned them, moving to a dedicated flechette platform with a proprietary magazine holding about 25 rounds. The rifle was a closed-bolt, gas-operated piston system that did not fit neatly into typical long-stroke or short-stroke categories. Flechettes required plastic sabots to fill the bore, and these lightweight sabot segments could depart the muzzle at high speed in unpredictable directions, posing hazards to nearby soldiers or even the shooter when firing prone. Flechettes also showed greater dispersion than conventional bullets, working against the program’s hit-probability goals, despite offering very low recoil and high cyclic rates.
Steyr’s ACR entry was a bullpup rifle visually similar to the AUG but with a more rounded chassis and a shroud that covered nearly the entire barrel. It also used flechette ammunition and sabots, reflecting the Army’s interest in dart-based projectiles. A distinctive feature was a chamber that moved independently of the barrel. During cycling, the chamber dropped down to receive a new round, pushing the spent case forward and out near the shooter’s hand, then rose back into alignment with the bore under spring tension for firing. Steyr employed polymer-cased ammunition with an aluminum reinforcement ring at the base and a primer ring around the bottom, functioning somewhat like a rimfire arrangement but in a different geometry. The flechette sat inside this case. As with other flechette systems, the plastic sabots could present safety issues for nearby personnel. The rifle supported semi-automatic, three-round burst, and full-auto fire, with emphasis on burst mode, and achieved a high cyclic rate of about 1,200 rounds per minute. Testing noted occasional polymer case ruptures, but evaluators believed improved materials and quality control could address that issue rather than condemning the design outright.
The HK G11, previously covered in a separate video, appears again here as one of the most mechanically complex yet reliable ACR entries. It used experimental caseless ammunition, where the propellant formed a solid block with a primer at the rear and the projectile embedded directly into it, often capped with a small plastic piece to keep the bullet centered during manufacture. There was no conventional metal or polymer case to extract or eject, eliminating several steps in the cycling process and promising significant weight savings for carried ammunition. The G11 fed its caseless cartridges at a 90-degree vertical offset from the bore, unlike designs such as the FN P90 that rotate rounds horizontally. A rotating chamber, likened to a small internal turntable, accepted rounds oriented downward, then rotated them 90 degrees into line with the barrel for firing. An emergency ejection port on the bottom allowed clearing of dummy rounds or misfires, but normal operation required no case ejection. Despite the intricate mechanism and concerns historically associated with caseless ammunition, such as cook-offs in a hot chamber, testing reported the G11 as highly reliable and not prone to those earlier thermal issues.
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