Over the last several years many new calibers have been introduced to the AR-type platform; from the .204 Ruger, 6.8mm Rem SPC, 6.5 Grendel, 7.62x39mm, 5.45x39mm, 5.7mm, .450 Bushmaster, .458 SOCOM, .50 Beauwolf and .499 LWR. These are just for the AR-15 platform; there is a whole other array to the AR-10. Of all those mentioned, the only one who has really done well is the 6.8mm Rem SPC. There are several manufacturers of rifles as well as ammunition. As of this writing this author could not find any ammunition….