foxtrot52,,,,,My thinking is the barrel could have been cut back a bit at the breech.. As the drum set farther forward than I would expect on an original rifle.. Also the drum looks modern,, This made it necessary to cut out the front of the old drum recess...The extra hole could be for the first spring. It does seem to a little further forward than normal. Yes it is original percussion...The protrusions on the front of the barrel could be to support a shade.It would have rested on these in front and the stock in the rear.. Just my opinion, as you know everyone has one..LP