I checked the Carcano web-site, and the spec for Oswald's rifle says the fixed sights are set for 300m, but it gets a bit complicated, as users are told to vary the position of the front sight "circle" within the rear sight V-slot. The V is made intentionally large, and positioning the front sight in the center of the V gives 300m; positioning it at the top of the V gives 400m, while positioning it at the very bottom of the V gives 200m range.
Seems that this was a cost saving measure for wartime. I'd previously read that some Carcanos were made with reduced barrel rifling, also for cost cutting, but I don't think Oswald's rifle was affected by this.
I wonder if Oswald was aware of any of this.