Note that although Pieper did not coin the name, both of these guns are built on a "Mono-Block" system, not the Demi-Block or Chopper Lump method. Pieper did inded build guns on the Demi-Block principal, just not these. On the upper gun "Diana" the block is bored on a slight taper & tubes inserted from the breech, which is the reason for the step.
On the lower gun "Modified diana" the tubes are stepped down & inserted into the block from the front. They only extend back about halfway through the block & may be threaded in.
