The rifle is set up for what we call Creedmoor matches, which were all the rage in the 1870s. The game was typically shot at 1000 yards. It was an international game and teams crossed the ocean to compete. Perhaps the two most famous ranges were Wimbledon in in Britain (Yes, it was a rifle range before it was turned into a tennis park) and Creed's moor on Long Island in New York. Imagine a 1000 yard range on Long Island.<G>
No artificial support was allowed and the back position was commonly used. One of the reasons the back position was popular was recoil. These were large caliber (.44 and .45) rifle shooting 500+ grain lead bullets probably around 1300 fps. The rules limited gun weight to 10 pounds so that made for a lot of felt recoil. Considering that these men were small by today's standards it is not surprising they adopted a more recoil friendly position.
The game is still played today, or more accurately, has be resurrected again. The back position is no longer used as the rules allow heavier rifles and artificial support.
Glenn