Brokennock
Cannon
Interesting idea. Might have to try it. I only get the slugging when I seal the side seam, and then not always. I figured the shot, having more mass than the paper, and least drag, would just outpace the paper cup and leave it behind. No such luck. I have had some success with the lubed cartridge similar to Blackhand's."If someone can figure out how to make these hold together just a little longer after leaving the muzzle, and drop away, without slugging, I'd love to hear how. "
Try using a dilute paste of starch and water. Apply it evenly to the paper before you roll it. Let the tube dry and it should hold together. Flour was a common buffer before the modern plastic shot buffer, so it should be safe for your barrel.
I'm really hoping a heavily lubed cushion wad on top of the existing cartridge, ala the SkyChief Special, gets me where I'm looking to be. Seems it would be the easiest next step to the quest.