5.7 is lethal enough, but armor piercing ammo for it is restricted. Nidal Hasan used a FN 5.7 to carry out the Ft Hood massacre of 14 in 2009. But it has not become a mainstream caliber, probably because most folks just don't see a need for it. 9mm, .40, 10mm, .357 Sig, and .45 will defeat...