I wanted to make a more appealing launcher. I ordered a fairly inexpensive wood rifle stock. After fitting the expansion chamber into the stock I mounted a plate on the front to bolt the bottomline adapter to. It looks the best using a 12 gram adapter but can handle up to a 20 oz tank. Field testing with 2" long Ballon shells was very consistent at about 280'. I still have a little cosmetic work to do. I never liked the look of the hose clamps people normally used to hold the barrel down, so I made it attach to the plate that the bottomline bolts to. I wanted to be a little different so I front mounted the bottomline adapter.
 

The wire wrapped around the barrel in these pics was just to hold
it in place while some of the pieces underneath dried.

The internals