So I got an idea the other day while reading about the Carl Gustav 20mm recoilless rifle, it's probably retarded but here goes.
Rheinmetall has developed a three-chamber 30mm recoilless revolver cannon utilizing the backblast principle, the RMK 30. It has a rate of fire of up to 300 rounds per minute:
https://en.wikipedia.org/wiki/Rheinmetall_RMK30Now, say that we downscaled this to between the 12.7mm BMG or the 20mm Vulcan (I was thinking a 15mm shell would be most appropriate, but there aren't any in current abundance. If I were going to choose one to mass-produce though, it'd probably be the 15.2mm Steyr used in the IWS 2000. The concept of a heavy machine gun/autocannon firing the 15.2mm Steyr has piqued my interest ever since I've heard of the type), and gave it the kind of crew ergonomics needed to fire it from the shoulder or lying prone. Have another soldier handle the ammunition belts and sighting, and suddenly you have a man-portable autocannon! Just beware the backblast and all.
Of course, 90% of the time it would be set to semi-automatic - it's basically a heavy anti-materiel rifle with rapid-fire capability in emergencies. Admittedly the external power source would be kind of an issue (Knowing that that was the main limitation of the M214 Microgun), but current advances in electric motor technology should make this less of a problem, in addition to the fact the motor is generally not engaged for long periods.
