FN America SS197SR, 5.7X28MM, 40 Grains, V-Max, 50 Round Box 10700016 The FN-designed 5.7x28mm caliber, standardized in 2020 by NATO, was originally designed in the late 1980s for use with the military issued FN P90 and FN Five-seveN pistol. With three decades of trusted use, the FN 5.7x28mm drastically improves range, accuracy and terminal performance from small arms with the hyper velocity bottleneck pistol cartridge.