.311 30 Caliber 238 grain FP 300 AAC Blackout. Hardness of 15. This bullet is tumble lubed only "Coated" Flat base bullet with no gas check. .311 diameter. Blackout suggested OAL 2.120. The first crimping grove is for the Blackout, second is for other 30 calibers. Blackout reloaders will need to inside neck ream brass to .311 for proper functioning in AR 15.