A classic indoor SMG. The da Vinci 229mm barrel is made for the MP5A4 and the Macaron bucking gives a flatter hop than stock. The 200 round Marui hi-cap is the real MP5 magazine for this gun, and the flash hider is made for the Marui MP5 muzzle. Example build by LoadoutLab. Every part is listed by its shop as made for this gun. Photo: "Tokyo Marui MP5A4 Airsoft AEG.jpg" by Dwt110, CC BY-SA 3.0, via Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Tokyo_Marui_MP5A4_Airsoft_AEG.jpg). The photo shows this gun model; the parts list is a suggested setup.