I used a length of grey schedule 80 pvc pipe with the end of it "capped" with cardboard cereal box taped in place like a little top hat over the end. Then a third of the pipe was filled with bad boolits wide enough to almost fill the inner diameter followed up with rolled up cardboard to hold the lead in the front third of my weighted sprue persuader. The end is taped to keep the plug in place. Works great, very durable and the tape can be replaced if it wears out after about a thousand or two sprue whacks.