6 mm XC

6mm XC (also known as 6XC) is a "wildcat" rifle cartridge, similar to the 6x47mm Swiss Match. 
History.
The 6mm XC was initially developed specifically for NRA High Power match shooting by 11-time NRA High Power National Champion David Tubb. It is touted as being one of the most accurate long-range 6 mm rounds in the world that is designed for repeating rifles.
The 6XC is a CIP standardized case (European version of SAAMI). Factory brass is available from Norma and Peterson.
Performance.
The 6XC is a 1000-yard cartridge, comparable to benchrest calibers such as 6x47mm Swiss Match, 6.5×47mm Lapua and 6 mm/22-250; it fits into cartridge class that exceeds the velocities of benchrest calibers such as 6mm BR Remington, 6mm BRX and 6mm Dasher. David Tubb has claimed several wins with the 6XC in NRA High Power National Championships and a number of NRA Long Range championship events (1000 yard events).