Experience.Why do think a 264WM with a 9" twist is limited to 130g bullets?
I have a few 264WM with 9" twists and all 3 factory rifles shoot a 142g ABLR just fine.
I also have a switch barrel I use for F-Class and a custom hunting rifle switch barrel both running 8" twist barrels and I also have a shipment of 7" twist Brux barrels on the way.
Cheers.
Can it stabilize 140g class bullets situationally? Yep, and some it would not at all in my experience. Is is optimal to shoot a 140g class bullet from a 9 twist? Nope. Can accuracy fall apart unpredictably at range due to marginal stability. Yep.
Respectfully, specific to 264win, I have had and shot through just about every variation of 264win a guy can imagine going back to the early 1990's. Including multiple custom reamers, a couple of gain twist barrels, custom twist barrels and several SAAMI spec rifles. I have played with several other 6.5's over the years as well. However, I have not yet owned a 6.5PRC so I can't comment directly as to its ultimate capabilities.