vigillinus:
The various public and exhibition trials of the day were well reported in the sporting press at the time, complete with published diagrams, and are discussed in Graeme Wright's book.

Personally, I think a serious scientific treatment would fail to find that more than one in ten shooters today, in the optic age, could hold any open-sighted rifle to better than 3 or 4 inches at 100 yards, for 10 shots.

I have one very accurate double, a Jeffery .400 3-inch, which shoots around 3 inches at 100 yards. NitroX witnessed it shoot both barrels into an inch or so at 50 yards off the 'standing post' 2 weeks ago. Here's a yarn about a hunting trip with that rifle last season:
http://www.hotkey.net.au/~orrs/LongShot.htm