Haven’t been on the for about as long as this post been old. I have from Short Lane Arms their “209 to muzzleloader adapter” in .410, 20ga and 12ga. They replace what would be a breech plug in standard muzzleloader. They have O rings to hold them in chamber. Just insert in chamber close action and load from the muzzle, several videos on YouTube showing the complete process. Sorry to say I haven’t had a chance to pattern them so farAftermarket breech plug! Also, apparently some guys have cut off the base of a hi-brass shell and primed it. Then they loaded the gun as a muzzleloader. I'm not in any way endorsing the practice...just wondering if anyone has tried it. Seems iffy to me, but there's guys on youtube that roll with it.