This is a Sig Sauer Stock, model STOCK-X-FOLD-M4-BLK.
SIG SAUER factory replacement M4 stock installs easily on your MCX/MPX via the receivers 1913 interface. This stock option gives you the ability to install standard AR-15 types buttstocks on your MCX/MPX. Stock is available in black. Note: Magazine holder is removable but does not accommodate MPX magazines.
Features:
Black finish
Side folding stock for MCX/MPX
Accepts all standard /AR style stocks
