5.7x28mm cartridge. Originally developed by FN Herstal for the P90 and Five-seveN system, the round was built around high velocity, low recoil, and compact-platform performance. Image Jens Hammer Every firearm is limited by the cartridge it fires. Some cartridges are designed for broad utility, while others are created to solve a very specific problem that demands a different solution. The 5.7x28mm falls firmly into that second category. In the …