I made a fully adjustable monopod that is easily removed , with zero modifications that will fit any hollow AR-15 grip . I made it for an Impact and it has almost three inches of travel . First step was to remove the existing hex bolt that holds the grip to the frame . I then cut a 4” long piece of 5/16” ready rod . Turned the one end down in the lathe and rethreaded it to M6 the same length as the existing bolt . Then I used a 4” piece of carbon fibre tubing 15mm OD x 13mm ID ( had this left over from a barrel sleeve job) . Inside the tubing I glued a length of 1/4” hose ( shop air line ) . Made a small foot for the bottom of the “leg” from some aluminium and glued it inside . Now with the grip reinstalled with the longer stud , the leg simply screws on . It’s rigid enough to hold the weight of the gun , and easily adjusted .