I suspect that my 180 grain 600 yard .308 rounds wouldn't be a happy combo, even in an M14... They were loaded pretty hot, but then again, I was playing at the time with custom actions, and we took a LONG time building up loads for that rifle... I really miss it. The primers were flowing a little, but weren't perfing...
FWIW, many benchrest competitors will run about 3420 fps with a 68 grain 6mm bullet - that's a known sweet spot/starting spot for working loads... You change the vibrational characteristics after that with seating depth. And yeah, we were starting with a touching the lands - not jammed... Jammed, if you have to pull your bolt with a life round, you can dump powder into your trigger, and that'll screw up your record target. Jammed does tend to do well, because it is consistent, but... Too much hassle.
And yeah - that is WAY over SAAMI for a 6PPC, but we were using custom actions and barrels...