The 6.5 mm Grendel (or 6.5 x 39 mm Grendel) is a 6.5 mm caliber intermediate cartridge developed in 2002 by Bill Alexander of Alexander Arms and Arne Brennan of Competition Shooting Sports. The 6.5 Grendel was designed as a low recoil, high accuracy, long-range cartridge for the AR-15 platform. The Grendel design philosophy was "start slow and end fast". High muzzle velocities accelerate barrel wear and increase the percentage of recoil due to escaping gases but only yield good impact energy if the bullet is efficient at carrying its velocity downrange. Constrained by the length of the 5.56 mm NATO round, but wanting to launch a much heavier bullet, the Grendel designers hit on a short, fat case for more powder volume while saving space for long, streamlined, high ballistic coefficient (BC) bullets that give up little of their energy in-flight. Firing factory bullets from 90 grains (10 g) to 129 grains (8 g), its muzzle velocity ranges from 2,500 ft/s (760 m/s) with 129 and 130 gr bullets to 2,900 ft/s (880 m/s) with 90 gr bullets (similar in velocity to a 5.56 mm 77-grain round).
