5.7x28mm 40 Grains, V-Max, 50 Round Box5. 7x28mm 40gr V Max 50 rd Box 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.