Hello Chris,
Your Berdan II is quite interesting. Nice find with the later pattern long range volley sights. They were added in the early 1880 after the experience gained during the Russo-Turkish War of 1877. Your rifle may or may not be an Austro-Hungarian capture. Generally, the Berdan's that were captured during WWI had the ersatz swivels added at a field depot or at an arsenal. Both depots and arsenals were well equipped and were swivels added to your rifle, the holes for the swivels would have been drilled round holes.
There is no question that your stock at some point in time had wire sling swivels added in place of the original Russian swivels, however the crude holes in your stock were not properly drilled. If they were Austro-Hungarian in origin they would be perfectly round. I'm guessing that this rifle was either Serbian or Bulgarian issued.
Warmest regards,
John
Here is the PM that you sent me I'll have to break out the camera and see what I can find on this rifle with what has been brought forth in this thread. I do know both sides of the butt stock has very faint round cartaches. Like I said I am not arguing just trying to find out how mine got this way and by whom????