The irony is that the first PDW concept in modern military history is US Carbine .30 Cal. M1. A few thousand M16s were ordered by USAF in late 1950s to replace M1 Carbines used by AF base guards at the time. So, eventually, by WW2 standard, everybody is using PDW today.

 

European style "PDW" is redesigned SMG with small caliber, high velocity rounds. Alone with some Chinese new models (which use some ammo of their own creation), those are new generation SMG that has some amazing penetration power against body armor at close range. I think we should ditch the concept of PDW and embrace what those guns are: new generation of SMGs.

 

And there is technically no reason why we can't design an SMG firng small caliber, high muzzle velocity with AR-15 lower. Just a little search:

 

Good thing about PDW's is concealed carry ability. People like Muammar al-Gaddafi or Fidel Castro could walk around accompanied by uniformed thugs carrying AK-47, but majority of modern politicians and businessmen would, probably, make an unwanted impression in public, if protected that way. Smaller caliber often means small size and smaller magazine that still has decent ammo capacity, and bodyguard can keep everything under the suit.

 

DG