I also have some experience with muzzleloading rifles and have a friend who has done some pretty spectacular hunting with a 12 ga smootbore here in the Rocky Mountains.
I am familiar with the Prussian tests and some the British did. My conclusion is that many physical qualities may effect the results of a smoothbore volley,i.e; quality of powder, quality (or consistancy) of cartridges, quality of the firearm, weather, wind, etc.. I suspect that the result counted more on doctrine and training. What was taught as a point of aim? I seem to remember an Austrian battalion firing over the head of of an attacking force because they were trained to fire streight and level and the attacking force was coming up hill.
As I remember my freind took a Rocky Mountain Goat at 80 yards using a 12 ga. flintlock Hudson's Bay fusil, but he was using a tightly patched ball in a clean barrel. I think the firearm had more potential then most of the people using it were able to exploit. You have to expect that the French and other skirmishers had learned this.
A rifle on the other hand has to incorporate all of the above or it is just a gun that's hard to load. There are any number of references to the training and effectiveness of the British rifleman, are there any out there on the Prussian shutzen?