Buzz Bee Ultimate Missile Blast Internals (including tank internals):
Hadn't ever seen the inside workings of a pull-pin tank myself, so dentured the dart and cut this one open.
The mechanism looks fairly easy to replicate with just one o-ring at the front and a tiny one on the pin at the rear forming the seal.
* Exhaust valve type: Pull-pin
* Tank volume: 60cc (75cc including connector-tube to the pump)
* Tank max. OD (at overlaping seam at waist): ø56.0mm
* Tank max. OD (main part of body): ø52.5mm
* Tank max. ID: ø48.0mm
* Tank max. external length (at valve seat): ø39.0mm
* Tank min. wall thickness: ≈2.0mm
* Pull-pin valve max. throat ID: ø11.4mm