I too would encourage you to check with BPI about the heavier bullets. I did and their response was that the 150gr magnum loads were limited to 400gr max conical. For larger bullets up to the largest powerbelt (I think that is 530gr) the max powder load is 100 grains.

Like what was said, call or email them for confirmation of that info so you have it direct from the horses mouth.

Good luck with your gun, my son's Apex is a real shooter also.