It virtually always depends on the load and all of the possible factors that can affect a shot and where it will hit the target. It's possible to have 2 shots touching with any muzzle loader and then to have the 3rd shot off by 1 to 2 inches.
Most people do not have the ability to shoot better than that off hand since those kinds of groups are usually made shooting off the bench and dependent on perfect conditions and loading with optimum components.
When trying to compare the performance of muzzle loading rifles, the shooter's component choices and ability are usually the limiting factors, more so than the choice between similarly priced rifles.
There's different scopes, loading & shooting techniques and practices that can affect performance. It's dependent on who is behind the trigger and doing all of the work, but under actual and ideal conditions a 1-2 inch group is a real possibility. While that's not a group size that can be fired anytime on demand, some guys can do it if they're really good. The more expensive rifles, with the best equipment and being fired by the best shooters off the bench can shoot such groups much more often.
While for others shooting rifles like the Wolf or the Buckstalker, pie plate accuracy at 100 yards is probably considered normal for as many shots as a person wants to take with a barrel that's swabbed clean in between each shot.
And so the group size can be anywhere in between 1 - 8 inches.
There will always be some amount of the group spreading either due to shooter error, components, conditions, loading practices, quality of equipment, cleaning regimen between shots, Ad nauseam
