i've done it on several guns. here is how i do it.
saw off the barrel with a hack saw. i use an aluminum square to make sure the line i follow is straight.
run some painters tape around the barrel where you want to make the cut and draw a line with the straight edge of the square around the barrel on the tape
cut on line, slowly and carefully.
then i use a flat file to make sure the cut is square, i recheck with the square.
you can use emery paper to polish out the cut or file marks, radius the edge and clean up the cut.
then drill, tap for your new bead . you can paint or cold blue the barrel at the cut.
i got a kit from midway for drilling , tapping and mounting the bead square.
mount your bead and your done.. its a 15 minute project really.