HK style Polymer made dust cover. 
 
*This dust cover is made for general GBB. It CAN NOT be closed on the MWS system, due to the thickness of the MWS's BCG design. The normal dust cover used on GBB and RS AR cannot close on MWS. 
You can put it onto the receiver. Just unable to close on the ejection port.
 
Made in Taiwan
BB type: 6mm 0.2g BBs
Power source: Electronic PTW 11.1v /8.4v
Power: 90 m/s = 0.81J with 0.2g BBs
J / cm2:  2.835 J/cm2
No primer using function