Maxim Defense MXM47839 Roller Delayed Blowback System Buffer Carbine converts a straight blowback AR-9 into a roller-delayed system. The Carbine Length RDB replaces the AR-9 buffer and spring, providing a drop-in fix for AR-9 buffer weight issues. The roller-delayed design delays bolt opening until chamber pressure drops, reducing recoil and improving reliability and accuracy. Not available to ship to California, Illinois, or Washington. Specs: Material Steel. Manufacturer Maxim Defense. Mfg. Part Number MXM47839. UPC 680017478391. Condition New. In Stock.