Cooper was dissatisfied with the small-diameter 5.56×45mm NATO (.223 Remington) of the AR-15, and envisioned a need for a large bore (.44 cal or greater) cartridge in a semi-automatic rifle to provide increased stopping power and one-shot kills on big-game animals at 250 yards. This became known as the Thumper concept, inspiring the development of the .450 Bushmaster, .458 SOCOM, .499 LWR, and the .50 Beowulf among other cartridges, all of them suitable for integration into preferably the AR-15/M16 rifle/M4 carbine or alternatively the AR-10/M14 rifle platforms.