The 5.7x28mm round is a small-caliber yet high-velocity round developed by FN. The most popular firearms chambered for its use is the FN P90 submachine gun and the FN Five-Seven pistol. Well now there’s a pistol called the Fort-28 from the Ukrain chambered in 5.7x28mm now too. The polymer pistol is double action and holds 20 rounds with a barrel that’s 4.5″ long. Check out the pistol maker’s site for more details. It looks like a pretty interesting design.