Assault Rifle/Bullpup - 5.56mm Discarding Sabot Flechette - Austria - 1250 RPM - The Steyr ACR was a candidate in the US Army's Advanced Combat Rifle trials.  While the outside appearance is very similar to the AUG, the internal mechanism of the ACR is very radical.  The use of a completely cylinderical cartridge corresponded with what engineers called a 'raising chamber'.  Upon firing, the chamber would slide down and a seperate piston would strip a new cartridge from the magazine into the chamber.  As the new cartridge enters the chamber, it displaces the fired case forward to eject it.  The light flechette projectile allowed the high cyclic rate to remain controllable; however, Steyr limited the design to three-round bursts.  Unfortunately, the design was plagued by excessive chamber pressures in the 70,000 psi range.  One of the prototypes exploded during testing.  Once the US Army announced that there were no winners, the Steyr ACR has not been heard of again. D.E. Watters