 The lightweight American 120 mm XM291 came close to achieving 17 MJ of muzzle energy, which is the lower-end muzzle energy spectrum for a 140 mm gun.However, the success of the XM291 does not imply the success of ETC technology as there are key parts of the propulsion system that are not yet understood or fully developed, such as the plasma ignition process.Nevertheless, there is substantial existing evidence that ETC technology is viable and worth the money to continue development.