That stock has already been sanded quite a bit, as can be seen in the photos showing the forend and lower band. In fact, the furniture is "proud" of the wood in every photo. Maybe your best bet here is to give the stock a good scrub with warm water and Dawn dishwashing liquid, (or one of the other degreasing methods mentioned here) applied with a stiff bristle brush. You'll probably get quite a bit of dirt and grease/oil out of the surface of the stock which can't help but to lighten it, and when dry carefully hit some of the splintering areas with 100 grit paper or slightly finer. Of course, once you oil it with BLOicon etc. it will become dark again, but not AS dark as before. Best of luck!