Marui MP5 Standard 50rd Magazine will fit all Marui, Classic Army, and ICS AEGs within the entire MP5 series – including but not limited to MP5 A2, A3, A4, A5, SD2, SD3, SD5, SD6, K, PDW, RAS. Full metal construction.
Consider opting for an additional magazine and also a dual magazine clamp to increase your skirmishing capacity. An auto-loader also makes loading standard magazines much much easier.