bsa,
Yes, powder capacity is only part of the equation, Longer necks help, but shoulder angle has a major effect. The 6.5-06 has a .321" long neck, but the relatively shallow shoulder angle directs hot gas in FRONT of the case mouth, which also has a major effect on throat erosion. In fact, it's why the .243 Winchester tends to fry throats quickly: The shoulder angle directs gas in front of the case mouth.
The 6.5 PRC's neck is .272" long, but the should angle directs gas just inside the case mouth. (The. 264's neck, by the way, is .254" long.)
My 6.5 PRC has almost 200 rounds through it and through my Gradient Lens Hawkeye there MIGHT be a a very slight amount of erosion on the sharp edge of the chamber just in front of the case neck. But there's none in the throat itself, much less the rifling.
