The 6mm HAGAR was derived from the 30 Remington and it has the same case head diameter as the 6.8 SPC, also a 30 Remington derivative. The cartridge was developed by John Harrison, a prominent match rifle shooter and Sid Goodling, a well-respected bench-rest gunsmith for  the 6mm Harrison and Goodling Automatic Rifle (HAGAR) in 2003. It was developed for rifles based on the AR15 platform. It has achieved success as a varmint and a match cartridge. Hornady made a limited run of brass in 2012. It was not available loaded. The wildcat 220 Thunderbolt is based on a necked down the 6mm Hagar case.