the tippmann internals all fit in a tube and are based around a center mounted blow back valve and a back cap. all you really need is a tube that that valve will mount in, a solid stop in the back for the spring and pin to sit in, and a slot to let the rod connecting the hammer and bolt together to ride in.
best way I can think of is to find a cheap tippmann somewhere and hack the body to an utter minimum and then fit that into the rifle
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