5.7x28 mm@Everything2.com

http://everything2.org/index.pl?node=5.7x28%20mm: "Fabrique Nationale was one of two companies (the other being Giat of France) approached in the mid-eighties by NATO planners to solve two distinct problems which arose with military small arms. The first was the ability to arm soldiers whose mission objectives called for the use of both semi-automatic pistols and select-fire assault rifles. The second was the need to combat the increasing proliferation of Level II Kevlar vests and PASGT helmets.
In the past, when a soldier went into a special operations mission, ve often carried an assault rifle utilizing 5.56x45 mm ammunition, and a sidearm which used anything from 9mm to .45 ACP. This was a fine setup, but it required carrying two different kinds of ammunition, and the weight and size of the other ammunition put a limit on how much could be carried. Further, if the primary weapon was a 9mm based submachine gun, such as a Heckler and Koch MP5, they would lose the armor-penetrating ability of the 5.56 NATO rounds.
Fabrique Nationale sought to solve these problems by developing a round which possessed excellent ballistics, small size, and would be equally effective when chambered in a submachine gun or pistol. They answered NATO with the 5.7x28 mm round. It was first demonstrated in 1995 with the FN P90 submachine gun, and later in the Five-seveN pistol.
There are currently three varieties of the 5.7x28 mm round. The raw technical specs of the round are as follows.
SS190 - Standard
Bullet Type - FMJ
Cartridge Length - 40.5 mm
Round Weight - 98 grains
Projectile Weight - 31 grains
Muzzle velocity - 715 m/s for P90, 650 m/s for Five-seveN
Penetration - 48 layers of kevlar at 200 m
L191 - Tracer (color coded red)
Bullet Type - Tracer
Cartridge Length - 40.5 mm
Round Weight - 98 grains
Projectile Weight - 31 grain"