AR Fixed Mag by Cross Armory.

 The AR Fixed Mag utilizes a plastic plug that is pressed in covering a screw on the mag release making it inoperable and permanent. The plug may be drilled out an a new one purchased should it need to be removed.

From Cross Armory:

 Cross Armory’s AR FIXED MAG is a modification to the company’s extremely popular SAFE MAG. Designed in California for weapons in heavily regulated states that require fixed magazines, such as New York, New Jersey and Connecticut, AR FIXED MAG will not release the magazine once installed.

Cross Armory’s AR FIXED MAG is consistent with the fixed magazine laws that state that the magazine may not be removed from your weapon in order to reload.  It cannot be removed from the weapon without the use of a drill or other power tools.

Permanent magazine locking system for the AR-15 and AR-10 firearms.

Quick and Safe fixed magazine device: prevents the removal of the magazine from your AR-15 or AR-10 rifle (without destruction of the permanent locking features) when properly installed

Quick, easy installation.

De-installation requires the use of power tools.

Designed for markets (NY, NJ, & CT) that require permanently fixed magazines for all AR-style rifles.

NOTE: Tightening a mag lock too tightly may cause failures in the CompMag. The CompMag can be squeezed by the mag lock device if it is installed with too much force. This may result in rounds or the follower not moving through the CompMag properly. Always check the functionality by placing a dummy round in the CompMag and ensuring it can move from the bottom to the top and back down, with no resistance, before using the plug on the screw.