During the 1980s, Italian firearms producer Benelli teamed with the Italian ammunition concern of Fiocchi Munizioni to produce a "semi-caseless" submachine gun design. "Caseless" ammunition firearms had gained considerable traction during this period and it was only natural for various gunsmiths to attempt new - and sometimes radical - workarounds to the issue of dealing with spent shell casings created after the completed firing action (the German Heckler & Koch G11 caseless assault rifle being a prime example of this, the gun designed to fire the entire round out of the weapon). The joint endeavor for the two Italian companies became the short-lived CB-M2 Submachine Gun which failed to sponsor any serious interest.
Key to the function of the CB-M2 was its use of the specialized single-piece, brass-encased 9x25mm AUPO cartridge (its shape not unlike that of the German 9mm Parabellum). The AUPO round featured a hollow base filled with the requisite propellant store (rimfire ignition) capped with a fulminate plug. During the firing action that involved a specialized lengthened bolt entering the base of the cartridge, the round was fired in the normal fashion with a side-mounted hammer and both bullet and base exited through the muzzle (hence its "semi-caseless" classification). The bolt was then reseated between rounds (stripping a fresh cartridge from the awaiting magazine in the process) through a traditional blowback operation common to many submachine guns. As such, the CB-M2 did not require the sort of complicated mechanical ejection process at the receiver as in conventional firearms resulting in a simpler internal design less prone to jamming. The weapon sported a listed rate-of-fire of 800 to 1000 rounds per minute, the weapon being fed from a 20-, 30- or 40-round detachable box magazine. Iron sights were fixed as the weapon was never intended for precision ranged fire. Overall weight was 3.40 kilograms.
Outwardly, the CB-M2 was nothing of particular note as submachine guns go. It was of a traditional design and layout with a rectangular receiver sporting sharp clean lines, an angled pistol grip with integrated trigger unit and ribbed forend with a short muzzle protruding from the end. Magazines were inserted ahead of the trigger unit in the usual fashion and a hinged, folding double-strut stock was included for a more compact/secure hold. Overall length with the butt extended was 26 inches while a length of 17.7 inches was achieved with the butt folded over the receiver. Beyond that, the weapon exhibited little in the way of ground breaking details though this was probably a good marketing move considering the nature of the design - the selling point being the revolutionary semi-caseless approach.
The Benelli CB-M2 was eventually evaluated by several interested military forces who entertained the prospect of a semi-caseless design. The weapon achieved a favorable standing in the subsequent testing though the required use of specialized ammunition ultimately doomed the project to anonymity as military forces ultimately lived and died by way of logistics. Benelli dropped the interesting CB-M2 from marketing sometime in the late 1980s and the weapon was never heard from again.