A GBB/AR15|M4 Spec Rear Stock Assembly originally found on the VORSK VMP-2M & MD. Slide & Lock on a compatible buffer tube  with slots to fit a cheek riser.
 
M4 BUFFER TUBE - this stock is compatible with AR15 GBB Spec Airsoft Replicas
 
LEVER ACTION - the underside lever will lock the stock onto a compatible buffer tube
 
QD SLING POINTS - this stock features three points to mount a QD Sling Ring
 
CHEEK RISER - a compatible VORSK Cheek Riser Kit is available