Introduced in 2008 by Xtreme Machining of Grassflat, Pa,[1] the cases, commercially produced by Bertram Bullets, have a length of 3.030" and a head diameter of 0.640".
The patent refers to a "dual diameter" aspect of the projectile, where the main cylindrical portion of the bullet measures 0.331", 0.001" greater than the lands of the rifling.
This both reduces driving force required for the high muzzle velocity as well as improves accuracy.
The .338 Xtreme possesses a full 50% more case capacity than a .338 Lapua Magnum cartridge, but it drives a projectile with a claimed G1 ballistic coefficient of 0.825 of like mass at only 10–12% more velocity from a similar length barrel when measured at the muzzle.
A small production facility and single-source manufacturing affect availability of both the weapon and the ammunition components, so it is unlikely that the .338 Xtreme will be adopted as a military cartridge.