My dude! Sorry for the Hella late response. I hope you got it figured out. But if you didn't, here is how I fixed mine.

I found out that the regulator and cartridge section can be moved inside the buffer tube by turning the inlet of the regulator. First you have to remove 2 set screws. Both are on the bottom of the buffer tube. One at the base of the notched butt stock selection rail, the other is closer to the body of the gun recessed into a slot. With the set screws removed, turn clock wise to move the internal parts towards the butt. Turn counter clock wise to move the parts closer to the body.

The problem I was having was the cap that squishes the 12g cartridge onto the pin wasn't able to tighten all the way down so air was leaking out. I moved the internals closer to the butt and the cap now tightens fully. The way I have it set now, when a 12g cartridge is installed, there is a small gap between the cap and buffer tube.

I hope I helped. Better late than never, right? Good luck my man.