RL26 is your friend. This info and more is also in the ELR section post on the 300 PRC. There's another gentlemen there that also found a bit of a sweet spot between 74 and 75gr of RL26 I believe.
all 5-shot groups, 31", 9.5-9 gain twist barrel, virgin Hornady brass, CCI 250, 50 rounds on the barrel so far. Chrono is optical style, 20-25ft in front of the muzzle, so I suspect speeds are actually a touch faster.
74.4gr RL26 3.680" COAL, 225 ELDM
ES- 22
SD- 8
Avg- 2899
74.6gr
ES- 11
SD- 4
Avg- 2915
74.8gr
ES- 17
SD- 6
Avg- 2924