There's a trick I found years ago that I like when doing the final sanding/fitting of recoil pads. I keep different grits of 1" wide emery cloth in my farm shop for obvious reasons, and one day noticed that the free paint stirring sticks that you get when you buy house paint are the same width. I glue strips of the emery onto both sides of the sticks, with contact cement. They last a surprisingly long time, and are like using a file, very controllable. I didn't figure there was much need for pics ....... it's pretty self-explanatory. You'll probably find, like me, that they're useful for other jobs besides recoil pads.
BTW, the sticks I get now aren't the thin ones with a little "handle shape" on one end, they are just pine slats cut 1" wide, about 12" long, and about 1/4" thick, much stronger than the old, thin ones. They're flat on each side, not curved like some I've seen.