The Knights Armament PDW really really cuts that fine line of why bother replacing a AR15 carbine with it...because by the time you hang all the stuff on it that seems to be in vogue, its going to weigh right back up to what a normal AR is going to weight....the fact that it was a 5 pound gun firing a reduced cartridge that cant be had anywhere, were the only two things that
made it different. Its size was not much different than Regular AR's
PDWs were only made to replace the 9mm submachinegun. And approx baseline 19inches in lenth is what makes PDW's valueble to people thats first duty is NOT shooting small arms, not weight, as long as its reasonable.
On the current USMC Cobra helicopter....a M4 carbine cannot be kept in the cabin, it has to be stowed in a outside bin....A HK or FN can be carried on the crewman, and will be findable in a post shootdown( if the helo is laying on its side and you cant get to the storage bin...then you have a pistol in a blackhawk down situation. The USMC have been testing both the HK and FN pdw's
A communications lineman, is also served better by something really short and handy when up a pole stringing wire.
The other problem/fix of simply cutting assault rifles down to 8-10 inch barrels is that it makes them really rude little bastages to shoot..especialy for a clerk typist,
cook, dentist, etc....as with anything something has to give.
PDW's arent ment for steely eyed commandos, they or made for support troops to have a decent chance at killing steely eyed commandos.