I'm fixing to gore somebody's sacred ox here, but that idiot over at RECOIL Magazine pushed one of my hot buttons, that being the FN and H&K PDW systems and their "magic death-ray" powers.
Folks, the FN 5.7 and the H&K 4.6 PDWs were designed for the use of personnel who either couldn't be bothered to carry a real rifle, or whose duties made the carry of a real rifle impractical. Cooks, clerks, supply, and the other rear-echelon types who are vital for running a war.
Both systems pretty much produce the same result: .22 Winchester Magnum Rimfire ballistics out of something that's too large to be a pistol, but not big enough to be a rifle.
4.6X30mm. Bullet weight: 40 grains. Muzzle velocity: 1900 FPS.
5.7X28mm. Bullet weight: 40 grains. Muzzle velocity: 2034 FPS.
.22 WMR. Bullet weight: 40 grains. Muzzle velocity: 1920 FPS.
Which sounds pretty good -- until you realize that the .22 WMR is okay on 40-pound coyotes, but most-assuredly marginal on anything bigger. And most enemy soldiers are somewhat larger than a 40-pound canid.
So, basically what you have with the FN/H&K PDW systems is the equivalent of a full-auto .22 rimfire that the folks who don't carry a real rifle can shoot at enemy troops (armed with the equivalent of .30/30 deer rifles) who get around, over, or through the front-line guys and start running amuck in the rear areas.
To boil that down: the FN/H&K PDW guns are there so that the generals awarding the posthumous medals can say, "They went down fighting" with a straight face.
They are not a "magic death ray" to an enemy soldier -- or thug -- any more than your grand-father's .22 WMR varmint rifle is a "magic death ray" to an enemy soldier -- or thug.