5.56 NATO Fiocchi 55grn 3240 fps - CaseHigh volume AR 15 shooters know the math buying by the case is the only way to keep your cost per round manageable without sacrificing quality. The Fiocchi 5. 56 NATO 55 Grain FMJ Case delivers the same fast, reliable performance as single boxes at a significantly lower per round cost, so you can train more and spend less. At 3,240 FPS, this load runs at the upper end of standard 5. 56 NATO velocity flat trajectory, reliable terminal performance, and