AsMs,
I will try to answer your questions. First the author of the Revenant book, Michael Punke, decided his Hugh Glass character was armed with an Angstadt rifle. The rifle was silver mounted and was marked on the top flat Angstadt, Kutztown, PA. (Berks, Co.)
When I was contacted by the first prop manager they were looking for an Angstadt rifle, and I had one on my web site. Unfortunately, that gun had been sold earlier. A few weeks later, I was re-contacted by a different prop manager; this was mid July. The movie was set to begin filming late August. We discussed the possibility of me constructing two matching Angstadt rifles and have them in British Columbia within a month. I felt that I could get it done, but the Prop manager did not want to chance it. He then looked over the other rifles that I had available and decided on the Bucks Co. rifle. I then copied all the carving patterns and constructed a second rifle the same as the first. The rifles were delivered ahead of schedule. During the course of our conversations I mentioned that Jim Bridger was reported to have carried a Shuler rifle (Bucks Co.) I think this may have helped in the decision to go with the classic Bucks Co design.
As to the time period of the two rifles, either the Angstadt or the Bucks Co. gun would be of the 1800-1820 period, and either would be appropriate for some of the initial forays into the Rockies.
In Rosenberger and Kaufmann's book, Longrifles of Western Pennsylvania, they mention that gunsmith Henry Wolf, who is first recorded in Pittsburgh in 1787, advertised for a runaway apprentice, Hugh Cook Glass, who left in 1795. Glass was reported to have taken a "common rifle" with him. Wolf is believed to have come from Virginia, and on the two known rifles by him the patchbox ends in a four petal flower as used in Virginia. His work shows other Virginia characteristics as well.
As far as I can tell there is no definitive evidence as to the exact style rifle that Glass was carrying when he was mauled by the bear. Eastern longrifles of all varieties were carried in the western expansion, some better suited to the task than others. I suppose theories and opinions will abound; right or wrong, this is how this gun was chosen for this task.
Ron