I found that, if your crayola barrel can accommodate this, simply remove the PVC and stick the dart 3/4ths of the way down the crayola barrel, such that only the tip of what would be a standard dart sticks out. My friends have reported that this hurts more. And if you have an old gun with a stock that doesn't work anymore, hack off the stock and stick it onto the back with gorilla glue/epoxy, some small planks of wood (like, 1"x5" pieces) and some screws. I get the feeling that hot glue and PVC would fall off the first time you drop the thing.
A few things:
2. I'll get some PETG later this weekend, and I'll chop a few inches off the barrel.
3. Yes, the barrel is where the turret used to be.
Just to clarify: I didn't use the duct tape to make the seal; I used it to keep the barrel on, and close to the top of the gun, where it would best line up with the oval. I used hot glue to make the seal, thanks.