Thank you for the additional information. It is most helpful for someone just starting out trying to do research with no previous background (as I am). I knew that I would be getting the weapon and knew it was used from Chancelorsville through the end of the war, so I bought the Stephen Sears book on tape and used my hour commute to listen to it. I experienced what I am sure you have and became totally fascinated, so started to research the weapon and the soldier who carried it.
Patrick Matthews was in the "Old 12th" New York and re-enlisted with the formation of the 157th after being mustered out of the 12th.
You are absolutely correct that the bands are held in place with screws. Being a total novice, the only tool I had to measure the caliber was a venier scale calliper. I could have easily mismeasured it by 0.02 inches -- I expect your are correct there as well. As for rifling, it is probably there (given the other characteristics), but is so minimal that I have to use my imagination to fill it in many places in the barrel (as I think about it, not too surprising for a rifle of this sort that has seen as much action as the history of this one would indicate). In most of the rest of the barrel it looks like scratches, but is too uniform to be random.
As for the source of the powder horn and shot, your suggestion makes perfect sense -- however, I really like the round, wooden, screw-top cannister the shot is in.
I believe you are right on with your information about this weapon and truly appreciate your patience in offering your knowledge to a total novice.