Here is one of the Specna Arms CORE series that come with the PDW Stock, the  RRA SA C07 PDW CORE... "The latest delivery from Specna Arms includes new CORE ™ replicas with PDW stocks! The PDW version is equipped with a collapsible stock almost entirely made of metal – the only exception is the polymer foot with a non-slip texture. A place for the battery is inside the dummy buffer tube. The dummy buffer tube will fit a LiPo battery with maximum dimensions of 15x11x115mm."