Whoa guys, alot of beads are screwed in, but some are pressed in (i.e: Rem 870 express).
If your bead is missing, clean the hole out with gun scrubber or something similar and see if there are any threads in the hole. If there is, get a bead with matching thread and add a drop of loc-tite and screw it in. If no threads, it shouldn't be much to have a smith tap the hole and put a bead in for you. Probably <$20 including the bead