OK...just got back from the range after putting the 1855 Root Rifle through its paces. The first thing to note is that I disagree with DGW's recommended ball size. They say .454, but I think that is too small. They seated with very little effort...barely (and I mean BARELY!) shaved any lead.
I switched to .457, which were much more satisfactory.
I also think that DGW's recommended 40 grain powder charge is much too conservative. You can barely (and again I mean BARELY) get the ball rammed far enough down to touch that small charge. I found 60 grains of FFFg to perform much better.
In fact the best groups I shot were with .457" balls and 65 grains of powder, which is a max load. That delivered 4"-5" groups at 50 yards.
Recoil is very minimal. The gun is heavy, the ball is light. But there is noticeable gas and powder spray from the barrel cylinder gap. That gap is tiny, but there was enough spray to make my face sting a little with every shot.
The biggest drawback to this rifle are the sights. The rear sight is good enough, but too high. The front is a low, narrow, pointed blade. It was very hard for my middle aged eyes to see. Groups printed a foot high with 40 grains of 3Fg powder, and about eight inches high with 65 grains of 3Fg. With 40 grains of powder and .454' balls my groups at 50 yards were a foot across. With a .457" ball and 65 grains of powder, groups were 4" to 6". With good sights I'd have cut them in half.
It is a fun gun to shoot, but if I were keeping it I'd have a big bead front sight installed.