well this has been speculated for a while....
Pics:
http://lagunshop.militaryblog.jp/e39245.html
Vid:
YouTube - ????? ??????? SOPMOD M4
Summary: M4 SOPMOD, blowback AEG, Full-Metal, functioning bolt catch, stop shooting after empty mag, cool looking battery, and Full-Auto Hi-Capa 4.3....