Your exposures look ok so what ever exposure calc your using is working for you. At 50mm a .3 pinhole is around the right mark so your .4 is not so far off to worry greatly. I would expect sharper pinhole image for this setup unless you where not using a tripod or other support. Maybe the material of the pinhole is to thick, I use a soft drink can and sand in back with some 1000grit wet and dry sandpaper. If this effect, which is not unpleasant is what your looking for then keep going. is an active pinhole site that you may wish to visit as well.