The square tipped blades on a Herc prop are for high thrust at low speed, useful for dragging the aircraft out of short unimproved strips. Problems of transonic flow at the tip are avoided primarily because the shape and therefore the drag of a Herc prohibits a really high speed cruise. Hercs cruise at around 300KTAS.
The Orion however, only operates out of longer hard surfaced runways and spends the majority of its time in high speed cruise and so has a rounded tipped props.
If you compare the two aircraft you will notice that the Orion has a much thinner wing and smaller diameter fuselage than the Herc, also the Orions MAUW at 135,000lbs is 20,000lbs lighter than the Herc.
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