For those of you that like a shorter buttstock on the M4.   I took a cue from previous pioneers in this task and did the same thing, but my way.   The following thread showed the buttstock cut in a miter box, then some thin pieces of foam were made to conform to the inner stock shape and served as dams.   The two sides of the stock were filled with Marine Tex putty and then allowed to dry, then sanded..........   http://www.benelliusa.com/forum/showthread.php?t=18699&highlight=