If you are referring to the 870 and it has the bead on the pedistal, you have a problem. The base and bead are silver soldered to the barrel as a unit. You can try to drill out the bead and try to tap it (6-48) but you may run into a problem.
When you drill out the bead it leaves a little bit of shaft in the base. When you try to tap it, the now hollow shaft breaks free and spins. At this point you will be sol.
Maybe I'm doing something wrong, but this seem to happen about 50% of the time.
Experience is what you get when you were expecting something else.