pheasant665,
In 2018 I had the opportunity to work extensively with rifles in both 6.5 GAP 4s and 6.5 PRC. Used Hornady brass in both, and measured their water capacity after firing, with the Hornady 143 ELD-X bullet seated to the same overall length. They essentially had the same capacity, within .1 grain--with the .1 edge going to the PRC. (The GAP's case body is slightly larger in diameter, while the PRC's is slightly longer.) Both held .2-.3 grains more water than the 6.5-06.
From what I have heard and read, Ruger was not involved the 6.5 PRC, only Hornady--but the cartridge was designed just before Obama was reelected in 2012, and demand for ALL ammo and handloading components went sky-high, and stayed there until Trump was elected.
