I think I can help with this one. The Electras have both Hamilton Standard props and Aeroproducts props. The Ham Standard blades are cast from solid pieces of metal (not sure what exactly). The Aeroproducts prop blades are hollow and constructed from two skins covering longitudinal ribs. From a manufacturing point of view, it is very difficult to produce eliptical pattern blades from the hollow construction method, hence they leave the blades squared off, but in the case of the solid blades, the manufacturer has chosen to round them off. They may have decided to do this for neatness or personal choice on the part of the designer, but it makes little difference. Flight tests were carried out using a Convair 580 which had one of each type of propellor and it was discovered that there was no performance difference whatsoever between the two.
At a day to day level, the Ham Standard props feel to be more responsive to power lever movements, and there are certain differences in the ways in which the props need to be handled.
The propellors are not interchangeable with one another - if a Ham Standard prop is removed from an aeroplane, it can only be replaced with another Ham Standard, not an Aeroproducts prop.
Hope this helps to some degree, although it doesn't relate specifically to the C130.