Parts laying around bug me and I really enjoy putting things together that were not necessarily intended to be assembled in the same device.
That said.... it is a 2240 tube and valve assembly. A Baker Big Bore breech assembly for a 2250 or Discovery. An Airforce clone 24" .25 Barrel and an adapter I machined to mate it to the breech. I did not have a hammer so I am machining an old 12 gram CO2 cylinder for a hammer ... currently at 42.4 grams. Will be using another 12 gram cylinder piece for the back plug / power adjuster. Probably will use a SPA CO2 bottle adapter for a power source. I hope for 400 FPS with a JSB 25.4 but that may be too much to ask from a CO2 power plant.
While I was playing with the 12 gram cylinders I discover some .68 caliber hard rubber balls I have just press fit in the bore of the cylinder when the bottom end is cut off so I machined a male foster at the small end and plugged it into my Ninja 3K regulated tank so I could launch the rubber ball. Yea I was uninspired by the Umerex 50 caliber "Home Defense CO2 Pistol" Steve Scialli showed in one of his IWA videos and it might have influenced the creation item somewhat. lol Edit: This ball launcher is equally unimpressive!
Mr. Axlesson might have started on his quest in a similar fashion at some point. lol