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
HPA adapter M4 charger for Hi-Capa series
Airtac HPA M4 Mag Adapter for Hi Capa – MasterShot Custom
STL file HiCapa to M4 - HPA Adapter・3D printing model to download・Cults
STL file GLOCK HPA/M4 ADAPTER・3D printing design to download・Cults
HPA adapter M4 charger for Hi-Capa series
STL file Hi-Capa HPA Angle M4 Adapter・Design to download and 3D print・Cults
SpeedSim: Overview Of The Primary Airsoft M4 Adapter - YouTube