Congrats on your first post! Just a wild guess, but my Model 1893 (made in 1893) was re-barreled, probably in the 40's with a model 36 barrel. It has an extra dovetail. I have read that this was common on rifles that the barrel had been shot out, or corroded due to black powder. Probably not an issue on the 22's but have no other even close explanation. Someone should come along with a much better answer than mine.