700s are noted for weak primary extraction compare to a Mauser or M70.
Installing an M16 extractor will cure that although it degrades gas handling.
I have done this with 3 700s and it makes the rifle far better.
The OP said it worked w/o the can fine. That kinda narrows down the problem to the can --- doesn't it ?
My GEMTECH ONE works fine on everything including 300 WM and 300H&H.
The PRC holds more powder and can run a bit hotter. The only explanation that makes any sense is that the can is retaining gas after the cases has "shrunk back" and that gas is backflowing around the case. Those of us who shoot cast bullets are familiar with this when the load does not have enough pressure to fully "obtrude" the case and you get blowback around the case.
Same symptom, different cause although extraction is not affected as the INITIAL pressure is far lower.
The simplest test is to handload some at 30-06 levels. I predict the problem will vanish.
I'm hardly a troll. Appears I understand far more about internal and external ballistics than those calling me names.