The plenum size is 12CC for all Stoeger XM1 Bullsharks. And regulator Factory setting for all calibers is 15Mpa This comes from the Stoeger XM1 Product Manager directly.
I love Nate's review of the Stoeger XM1 Bullshark. After every shot that I take with it out of the box, nothing changed but thoroughly cleaned, I can't help saying "unbelievable" at th accuracy and very low SD.
When did you buy it and what has Air Venturi and/ Pyramyd Air told u? In my experience, Pyramyd Air has the best customer service in the Industry. Let me know, maybe I can help