Yes, believe it or not, this Pistol-Rifle system, which I spotted at Milipol 2009, converts any standard pistol into an assault rifle. Gimmicky? Mostly.
Built by CAA Tactical, it adds a stock front grip, picatinny rails, sight/scope and extra mag holder, while being compatible with a silencer. But it doesn't extend the barrel, for instance, nor can it replace pistol ammo with the larger cartridges assault rifles use for range. Nor can you go from semi to full auto, of course.
It may not turn your pistol into a true rifle, but the Pistol-Rifle converter does make the pistol more steady and therefore more accurate. I unfortunately did not get to actually use it, unlike the guy in the video below, so I can't say for sure if it really helps. [CAA Tactical]
Apoorva Prasad is a freelance writer and photographer based in Paris, France, who recently covered the Milipol 2009 military-police expo for us. He has a thing for holo-scoped assault rifles, and he sounds disappointed when admitting he's never been Tased.