5.56x39mm Firebrand Epsilon

This cartridge is the fastest of all the cartridges I've ever designed. Using the Knox powder, this cartridge pushes a 90-grain .22 caliber bullet at a blistering 3550 f/s for 2500 ft-lbs of energy, the same as that of the 7.62x51 NATO, all in a package the size of the 5.56 NATO.