FN 5.7×28mm [SEP] manufacturer
FN 5.7×28mm
The FN 5.7×28mm 
(designated as the 5.7 × 28 by the C.I.P.) is a small-caliber, high-velocity, smokeless powder, rebated rim, bottlenecked, centerfire handgun and rifle cartridge designed and manufactured by FN Herstal in Belgium. It is similar in length to the .22 WMR (Winchester Magnum Rimfire)(5.7×27mm)and to some degree similar also to .22 Hornet or .22 K-Hornet. Unlike many new cartridges, it has no parent case; the complete package was developed from scratch by FN.
mm Parabellum cartridge. The tests compared the relative merits of the FN 5.7×28mm cartridge and the HK 4.6×30mm cartridge, which was created by German small arms manufacturer Heckler & Koch as a competitor to the 5.7×28mm. The results of the NATO tests were analyzed by a group formed of experts from Canada, France, the United Kingdom, and the United States, and the group's conclusion was that the 5.7×28mm was "undoubtedly" the more efficient cartridge. However, the German delegation and others rejected the NATO recommendation