I don't want to take over snakerbot's thread so let's move this here.
Support for Constant-Force Spring pair (21lb total draw).
Support for ESLT extension spring.
Support for any 11-inch compression spring.
The plunger rod is pushed backwards into the plunger tube by the foregrip.
Redirect piece attaches to the backside of the grip frame.
Redirect piece is a pipe coupler, pipe plug, and a polycarbonate disc to act as a stop for the plunger head. The barrel output is a 5/8" hole with a 1/2 CPVC stub glued into it.
Trigger is the same as a plusbow Rev.3, just backwards and on the opposite side of the grip frame piece.