Quite possibly the easiest thing to do would be to get a .400 OD rod of teflon and then cut down little pellets to length, then drill them in a jig with a drill press to .22, then cut a X dead center from the top. It would be best to first put the teflon rod in a lathe and shape each sabot first so that there is a relief area so that the petals can peal back easy and lathe away some of the base so more powder will fit and bevel the OD of the mouth so it will feed best then cut each one out, drill, and countersink the mouth so the wind catches the petals and slows the sabot and peals the petals back. It could be done pretty easy but it would take some time to get the jigs made and dialed in with a little precision. I'll try to remember to pick up some teflon rod next time i am out and about.
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Reality always takes precedence.
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