I have been working on this for a few years. It's a spool valve gun/dump gun. Not really sure of the difference. I started working on valves of this type in the 90s. This is the current version. The barrels are interchangeable. Pictured here with 34" .45 caliber barrel. I'm still working on some videos for this on my youtube channel. Stay tuned. I'll update when I get them up. Thanks