I've killed deer cleanly with my .54 flintlock out to 125 yards and a patched ball...
Here is where I have an advantage, she has a 38 inch barrel..
Once I had cataract surgery, I did open up the rear sight which helped see the front sight, I had a very fine sight picture before...
Also, sight in about 2 inches high at 50 and then practice further...With mine I'm sighted in at 75, about 3 inches low at 100 and about 6 inches low at 125...