I use brass rod, and turn it down about .020" less than bore diameter. I cut 3 grooves in the rod, about .050" deep, 1/8" wide. Center drill, tap drill, and tap a hole about 1/2" deep. Clean out the hole, use locktite or super glue, and thread a 1.000" long, 8-32 or 10-32 Allen screw into the hole until it is tight. Cut off the screw head and file the end smooth, leaving about 1/2" threads. Cut off the brass jag about 5/8" long. I sometimes put the jag back into a collet, and cut a dish in the end so I can use the jag on the end of a ramrod to push the ball down.