Check Nelson's Submachineguns of the World (Vol 1) for the Reising drawings. (my darn HP scanner doesn't work).
The Reising model 50 is a delay blowback .45 smg of WW-II fame. The bolt is cylindrical in a thick-wall steel tube receiver. The bolt tilts up at the tail end into a recess area in the receiver tube. The tilting is caused by a small cam edge on the op-rod working on the bottom side of the receiver through a slot.
The op-rod is also the cocking device and is spring loaded. It is not gas activated. It is a simple delay system. The op-rod is a welded-together fork-like steel strap thing. They sometimes broke at the weldment but can be rewelded better with today's processes. The Garand op-rod is also a welded assembly by the way.
The levers are actually the trigger sears that release the op-rod and striker hammer (closed bolt system).
The Reising is a simple and unique design that could have been an assault rifle had there not been such opposition to an AR round by US military brass.