With regard to square tip props:
Square tips are less efficient than eliptical tips, and weigh more. They are, however easier to produce, and have plenty of waste material that can be removed (filed) when the prop experiences leading edge nicks - probably a factor on the C-130 as it is designed for low grade strips. As the thrust produced at the tips is minimal, the efficiency loss is low.
Silkhands, your comment applies to props ( "P-factor" ), but not jets (although the bit about momentum is out of left field). Sorry.
[This message has been edited by Checkboard (edited 07 August 2000).]