6mm BR (left), and .222 Rem (Right)

The .222 Remington was once the darling of the benchrest crowd, until it yielded to the superiority of the 6PPC. However, a "wildcat" version of the .222 Remington was adopted as the case for our 5.56 military round, so the .222 Rem lives on as the progenitor of the .223 Remington.