I know a lot of people hate the Primary Airsoft adapters, but when it's 110° outside, a light kit is a life saver. Also a great first step into HPA : r/airsoft
TAPP Airsoft Tapp M4 Adapter for Hi-Capa | Modular Series
AVA Hi-Capa To MP5 HPA Adapter Available | Popular Airsoft: Welcome To The Airsoft World