We’ve replicated a Hi-Capa magazine, and adapted it to take HPA, fed by 30 round shotgun shells. 

• Easy access, yet low profile magazine release at the rear of the adapter.
• CNC Aluminium magazine baseplate with a choice of colours adding flair to your build!
• BB latch to prevent dropped BBs on reload (0 BBs are dropped when an empty shell is ejected).
• High internal volume for good FPS/PSI.
• Works best with CYMA Shotgun shells, available on the website.
• US Style Fitting as standard. EU Fitting available here

The adapter comes with a 15cm airline, which can be cut down to your preferred size, and a blackened Foster 22 (US Style) connector fitted.

 To finish your adapter, transfer your feed lips and outlet valve from your Hi-Capa gas magazine. All adapters are pressure tested before shipping. Does not require modification of your pistol, insert just like a regular magazine

You will likely find that sites that do not usually allow HPA adapters in pistols, will have no problem with these adapters, due to their low capacity, and covert profile.

Instructions can be found here along with a brief video overview