We can't tell what exactly is the customisation done with this GBB-R from WE and we cannot say if throwing an extra magazine makes it a custom job. If you get one from Gunner Airsoft, drop us a note why. It'll make you about US$296 poorer... "Custom KAC PDW Gas Blowback (with marking)(with 1 extra Mag).  Customized from WE. Comes with two mags: one in KAC style and one in normal 5.56 style."