CSU is from Shirow's Ghost in the Shell manga. Which probably is inspired in other concealed weapons. IIRC he also used briefcases to hide SMG in the anime, but different style. (Nice CP2020 site I found, BTW)
There are also other cases built using Ingram mac-10 and mac-11s, in addition to Uzi based ones. The 70s were a different time (cold war games were in full effect and most of these relics belong to that time - up until the late 80s when the cold war ended.)
While it was better described in a Movie with Jet-Li there are EVEN "Executive Protection Briefcases" that hide Sawed-Off shortened Assault Rifles (a "Colt Commando" whose signature "M16 handle" was masked as the case handle). . . Other small, compact "Mini Combirifle Cases" hide Cetme / Fal (Spanish - French) 5,56mm. Rifles; they are used by Special Forces of Militarized Police of France (GIGN) and Italy (GIS of the Carabinieri) in VIP security details. . . Most recent iteration of the gun case I have seen was of British Mercs hiding HeK G36 rifles in small and compact "Ballistic Protection" boxes. . . The examples I have given, though, need the case Opened, stock extended and OFTEN had the Ammo Clip NOT yet inserted (for safe carrying purposes); the one of the OP needed JUST a safety button released and could shoot from "Close Position" without too much of an hassle (needed opening to change the Clip, nonetheless !!). . .
Then there's the film Desperado with guitar cases containing machine guns and even a rocket launcher!
Desperado 1 and EVEN 2 (Flamethrowers and "Wheel Bomb Kamikaze" Drone) are a little absurdly going, but there were HYSTORICAL representation of a Wild West Bandit that successfully had hidden a functioning Wincherster Lever-Action inside a "Southern Belle Banjo". . .!! The Shirow "Cyberpunk Gun-Case" seems to be anyway a sawed-off barrell Machinegun or even a Belt-Feed Combirifle, but obviously with the WEIRD "Liquid Metal Magfield-Shaped Bulletts" fired by "Hyperpowers Railgun Weapons" rather than CASED AMMO FIREARMS there are ALL MANNER of Shehanigans. . .
Yeah, that one was a little over the top. Just a little. I liked El Mariachi better, with the top of the guitar hiding all the hardware inside the case.
