The 6.5 PRC is basicly a 6.5 06 in capacity. Factory spec are about 2950 or so with a 140 . Factories are not underloading this. Only way to achieve 3100 with a 140 grain slug is to push pressures, gotta be 70,000 psi + to get those speeds.
Better get ahold of Hornady before someone blows themselves up:
https://press.hornady.com/assets/site/hornady/files/load-data/6.5-prc-v2.pdf
