You give pretty decent specifics and I don't see any reason this should not work, BUT maybe the bow just doesn't like those 500's. If you have any give a 400 spine a try or take a turn off the limbs to see what happens.

I shoot 500's at the same weight (roughly) and 27" with great success so can't give a definitive answer. Of course the bow shoots a 300 spine almost identically.