I recently converted a Mossberg 500A shotgun into a bullpup configuration using an aftermarket stock kit. The slide grip texture and ergonomics left a lot to be desired so I decided to design an adapter that would allow a Houge rubberized overmold forend grip to be mounted to the slide. I was going to design end-caps that would be secured to the core via bolts that would thread into inserts in the core. I have yet to design the end-caps and probably won't since this concept was ultimately abandoned in favor of an aggressively textured polymer one piece design: http://www.thingiverse.com/thing:789051. However, this concept might be useful in attaching a Houge grip in a more generic manner, such as to a picatinny rail perhaps (note: current design has recessed bolt holes that will only allow mounting to the specific bullpup stock kit slide used). If anyone would like to remix in that direction please let me know via comment and I will gladly provide the CAD file.