The S330 peepsight is an option on Mossberg. 22 rifles of the later period. Most of my Mossies are the earlier period, using the S130. They have different receiver diameters, thus aren't interchangeable.
My 640KD Chuckster wears a scope. It has the standard barrel mounted rear sight.
An okay shooter, but not great. Stiff trigger, not adjustable. A good reliable rifle. I paid $175 for it, but that was 20 years ago.