I just bought a Magpul MOE handguard, and unfortunately it has sharp flashing running along the entire length of both sides of the bottom half, which digs into my hand and doesn't feel very comfortable. I was considering trying to sand it down but I'm concerned about how it'll look afterwards. Has anyone ever done this? If so, is there a specific sandpaper type or grit you'd recommend for the task?

Maybe try a razor blade before sanding.  It'll be a little more precise shaving down the flash than sanding the whole area.

where did you buy it? possibly a fake. if you think it's the real deal, post in the magpul forum before you mar it up, they'll probably replace it for you.

http://www.ar15.com/forums/f_2/124_Magpul.html

if you bought it from a potentially sketchy seller, i'd go the refund route.

if you insist on sanding it iv'e done it to an afg2 and it came out alright just use the highest grit sandpaper you can find.

On polymer items w/flash, I gently use a fine-toothed rattail file and it works great, just don't get too aggressive w/the file.
Tomac

My concern with using a razor blade is that I might gouge the plastic. The flashing is literally only a couple of hairs widths tall.

I bought it from Combat Armory. I guess it could be a fake, but if it is it's a good one because to me at least it looks pretty legit. I might ask in that Magpul subforum, thanks for pointing it out.

sauceboss and Tomac, after sanding/filing, did you notice any difference in the finish? Did it look like you sanded or filed it? The handguard is of course black so I'm concerned that in the area I sand or file it it'll look like a light gray/white line along that area.

Use a knife blade at 90* angle. Flashing scrapes off easily and that way you won't gouge the plastic.