Finished breech load mechanism. It's too complicated for pictures, so I'm making a video. It's my silencer piece shoved down to the bottom of the barrel, then my scope after that. the scope is connected to a spring, which holds it in place until you put the dart in the hole in the barrel (which i also added a tube to go inside the dart, should help air loss), and then you release it and it snaps back in place.

EDIT: I tested it, it may still work, but my trials did REALLY bad. The hose exploded twice, and the air started leaking out from the handle? I have no idea why. I will continue to try to fix these, but i might need to start over (with the gun at least)