Inspired by fineredmist_7's post:
So, for what it's worth I built one yesterday. It's a neat concept and silly quiet, Fiocchi 209 were pushing a 14 grn lead round ball around 700 fps and a federal 209A were a touch over 1000 fps. Only problem is accuracy, minute of soup can at 10 yards but that's about as good as it gets. I thought I'd have some fun so a reamed the bore to .245" and tried it smoothbore with .250 roundball for the same effect. You can also muzzle load it as a shotgun with a 4 or 5 grains of FFFg to deal with those pesky bumblebees. Pretty useless past 8 yards though 10 max. Kind of a neat novelty but is does not perform satisfactorily enough for me to be excited about it. If anyone else tries or has tried it let us know your findings. Most of what I have read about roundballs being powered by a primer of some sort has reported less than stellar accuracy.