Ahhhh....the classic question!!!
Mate,
I will endeavour to find the official answer to that one (I have it somewhere...a Lockheed Digest on propulsion) but in the meantime will rely on my memory...
Although both powered by the T-56 I think it comes down to the roles of the aircraft. Although the C-130 is employed at low level, originally it was designed as a strat aircraft with pretty much the prop shape used (albiet three bladed originally). The P-3 however was developed from the Electra (square-tipped) specifically with sustained operations at low level in mind. I believe the rounded tips provided better efficiency at lower altitude for this particular powerplant combination that the square tips of the Electra. Don't ask me the aerodynamics of that one, I have an Arts degree!!! Bear in mind this is my memory we are relying on here.
Incidently I was told once that P-3s park with their blades in a + so the blade tips are not at head height so as too prevent people from headbutting them, and C130 props are x-ed on the ground for the same reason...as they are mounted higher. I noticed you spelted CC-130 which means you are either dyslexic or Canadian, perhaps where I have written P3 you should insert CP140?