The magazine tube can stick out though because that is inevitable. I can't tell you why it has to yet. It is a surprise... 
Anyway, that is why I design all compact valves... such as the BFB style pop off thingymajig.I can't draw good springs in sketchup, but I figured you understood there was one because of the previous designAssuming there's a return spring in there somewhere, looks like it would work
Do you think it HAS to be pulse air? Would a blowgun be enough? I mean, once the piston loads a round, it won't some back until it shoots because I'll hold the trigger down until it pops. Then I'll let go and let a new round fall in.It will cycle like mad or not at all with constant flow, but for semi auto with pulse air it should be perfect.
Jack you posted good diagrams but they won't work in my application and I also like servicability... I don't even think I can make any of those anyway
