If you want to use an MP5 magazine instead an M4 one with your HPA-powered Hi-Capa airsoft pistol, you're in luck, an adapter is available from AVA Airsoft... "We are happy to announce that the adaptor is now on sale. Working pressure up to 150 psi & slim design to fit with all hi-capa magwells on the market.

Featuring anti bbs flow back system, BBs single stack guid, CNC aluminum valve (EU & US). Compatible with Marui, AW, WE, Golden Eagle & Guarder ultralight mags that can be pre-installed on order."