The 44 Remington Magnum cartridge is loaded with a 0.429-caliber bullet, and a 44 Remington Magnum revolver has a bore diameter of 0.417-inch. Neither has a damn thing to do with 0.44 caliber.

Those calibers fall between the current 7.62 mm and 5.56 mm rounds and include the .260 Remington, the 6.5 Creedmoor, and the .264 USA, as well as other variants that aren't available commercially ...