This is my own design for how to single a Nerf Sledgefire. You will need to cut the very end of the pressure tube off for the pt adapter.
The piston adapter is designed as a drop in to go in the end of the piston.
There are two options for the singling barrel, one for brass and one for cpvc included. Mount one flush with the end of your barrel to make contact with the pt gasket.
I use one of the silicone gaskets from the caliburn etsy page as my seal from the pt adapter to the barrel adapter.