The PDR was a concept gun Magpul prototyped years back. 5.56 bullpup, fed from standard NATO mags, full ambi controls, selectable ejection side, long enough barrel to give decent velocity/muzzle energy but being a bullpup also small enough to fit inside helis, tanks etc for crew defence. Modern take on the L85 Carbine (L22) basically, would've been pretty awesome I reckon but they never went beyond a couple of early prototypes.