Yep, single tube blowback. Not like a modern Tippmann though. More like a giant metal Stingray. It has to do with the way the air is routed through the valve. There is a choke type velocity adjuster accessible through a hole in the right side linkage arm cover. The hammer is rather huge, with a main spring that looks like it was out of a shot gun magazine.
I'm inspired to finally fix that valve leak, I should be able to get some disassembled pictures sometime this week.
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