Poseidon HPA Series Stormbreaka GBB M4 Adapter for G Model / Hi-Capa GBBP ( HPA Only )
Primary Airsoft Hi-Capa M4/HPA Adapter | La Capa Customs
Primary Airsoft HI CAPA HPA / M4 Adapter for Tokyo Marui Magazine - Airsoft Extreme
Amazon.com : SS AIRSOFT Primary Airsoft HPA/M4 Adapter | Hi Capa Airsoft Adapter (Tokyo Marui, WE Tech/Armorer Works & Novristsch/KJ Works) : Sports & Outdoors
Primary Airsoft HI CAPA HPA / M4 Adapter for Tokyo Marui Magazine - Airsoft Extreme
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
Amazon.com : SS AIRSOFT Primary Airsoft HPA/M4 Adapter | Hi Capa Airsoft Adapter (Tokyo Marui, WE Tech/Armorer Works & Novristsch/KJ Works) : Sports & Outdoors