I found a guy who sells on GunBroker, that makes Lee Drive Key slugs. Basically the Drive Key slug is a Nessler Balle with a "rib" in the base.
Using my .680 sizer it seems they drop from the mold a little bigger than the molds advertised .680 diameter.
I'm trying to decide if using these in a thin masking paper cartridge I designed last year is worth it vs just hand lubing them and dropping them in like Minies
From what I recall , I saw no difference last time ramming bare .678 slugs down
my .69 bore vs patching them with paper.
The .010 of windage probably won't matter as much in a smoothbore especially when it gets fouled, and paper might just add an unneeded element of failure as I also recall the paper tearing off of the slug in a fouled bore during my last experiment. If the .69 Rifled Musket uses a .685 Minie then .680 seems perfect for a smoothbore.
I guess I'll just have to get out and try it