BOLT-ACTION, BREAK-OPEN BREACH
This design allows direct access to the breach for the manual loading of spuds or specialty rounds.  When the bolt is retracted, the breach is raised a few inches, providing unobstructed access.  It requires a hefty frame, so I doubt it could be man-portable, although, a really big-ol'-boy might be able to weild it.  If this were turret mounted, one man could fire it as fast as the chamber could charge. 
The barrel and guide plate pivot around a pin in the foreward hole. As the bolt is retracted, The operating rod runs back through the guide plate slot, thereby raising the breach for ease of loading.
Some people have told me that the metal parts for this design would require custom machining and, therefore, be very expensive.  This isn't the case.  With a cutting torch, an arc welder, and some scrap metal you can fabricate all the parts yourself, along with just about anything else.  I built a preliminary version of the guide plate with old junk I found behind my barn.  It just takes a little ingenuity and some skill.  If you don't know how to use a torch and welder, I strongly suggest you learn.  Many community colleges offer metallurgy courses that teach these invaluable skills. 
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