First of all I can't fully claim this as my own. I did see a chamber set up like this one on this sight that dealt with semi auto by Mr. Plow. However, that post did not go in too much detail as to what or how those tubes and regulators were used. So I made my own version
. I first had to figure out the action. I used 3/4" CPVC inside 1" CPVC. The 3/4 " is just the right size with enough clearance to slide inside 1". Check the diagram below.The chamber section has an additional secondary air tank made from sch 80 PVC. It stores air at a certain pressure to blowback the action. The gauges might seem confusing, so here is their purpose back to front. The first gauge tells me the overall pressure of the cannon. The second gauge is a regulator to limit how much air gets into the second chamber.
The third gauge is a flow control. When you reduce pressure on a regulator or the air going into it, it equalizes the air or gas and bleeds some of it off. The third gauge with the flow controll slows down the air leaving the secondary chamber. That way there is still enough pressure left to recycle the next round. see picture for details.
There is a second blowgun on the cannon. It acts as a valve to the homemade air ram on the side of the barrel. It is setup to release air into the air cylinder after the cannon has fired. I know there are otherways to get semi auto, but I do not have access to a decent lathe. So this is the methond I chose. Anyways here are a collection of pictures of the setup
. Exploding metal is not good either, but at least it will hold up better than plastic.
I will say at this time that GGDT was not at fault but my own human error element. GGDT after all is a tool to help us get more potential out of our projects.