United Defense Mfg Corp's S9-DBB civilian semi-automatic carbine is a pistol caliber carbine inside an AR-looking rifle chambered in the time-tested 9mm NATO round (9x19mm) and designed to hit point targets up to 150 meters. The S9-DBB semi-automatic carbine of United Defense takes after the AR-looking rifle designed by Eugene Stoner but using the 9mm Glock magazine and other after-market 9mm Glock-style magazines. It uses the very simple delayed straight blowback system influenced by the design of Ferdinand Mannlicher in earlier years. In this design, the breech block is delayed after the round is fired to make sure that the ammunition cartridge is fully supported while under high gas pressure. UDMC did not design the system using the rotary or roller delayed blowback as it believes it is unnecessary, adding more moving parts that will be subject to wear and tear while the weapon is in battery.