One of the most popular PDW weapons in the rifle caliber revolution has been Sig Sauer’s Rattler. The small 5.5″ barreled carbines fit in equally unobtrusive bags and deliver far greater control, kinetic energy, or both to the user than weapons like the Uzi or MP5K.
The 300 Blackout round, delivering a more efficient and accurate approximation of .45 ACP energy in subsonic, has been a popular addition to the AR world for a couple of specific circumstances. This is one of them.
The NSW Rattler receiver is an M4A1 mod, meaning it doesn’t come with a serialized lower and fire control, it instead drops onto an in inventory M4A1. The upper itself is still the self contained firing unit it has always been and even with a can attached at the muzzle it offers a discreet and maneuverable weapon for the user that far surpasses what something like a Mk. 23 could efficiently do.
Inferior Rifles is a newer and smaller channel, however they do clones and do clones well. They break down the NSW Receiver, a discreet PDW/PSD type take of the CQBR concept, here in the video.