The LaRue Tactical R.I.S.R. is a new and interesting approach to an old problem. The charging handle of the AR family of rifles runs along the top of the stock when it is extended. If a user of one of these rifles wants to install some kind of comb riser to their rifle they needed to install it close to butt of a fixed stock or run an adjustable in the last position. If it is installed too close to the receiver it will interfere with the function of the charging handle which is obviously unacceptable.
The R.I.S.R. is designed to slide with the charging handle. It bolts onto the Magpul CTR or MOE stock and allows the stock to be put in a variety of positions without interfering with the charging handle. The folks at LaRue claim that the R.I.S.R. was built with the worst case scenario in mind and they have tested it with sand, dust, dirt, and more without being able to make it seize.
A product like this is especially needed on the LaRue Tactical OBR. The OBR has elevation built into the receiver rail which can cause optics to sit quite high. Until now, OBR users were stuck with comb risers on fixed stocks or on collapsible stock in the fully open position. The R.I.S.R. should give them some much needed options.