I have a single shot model 15A. It is the same single shot bolt action rifle. the rear sight is rectangular with a simple elevation adjustment. The front side is a blade with a pin size bead at the top.
Of all the rifles I have acquired over the years, it is my first and favorite. It has sniped out more critters, tree rats, birds, and stray cats than I can remember. Mine was given to me when I was 8 or 9 years old by my dad. It was given to him when he was 7 or 8, so I would guess it dates to 1948 or 49 if not before.
Just thinking about that little gun makes me smile.