I am wondering why Hevi-Shot Mag Blends kick so much harder than the hevi shot #5's, 6's or 7's in hevi- shot?

They have the same powder loads.

I have shot the Mag Blends before and I went to shot a couple through my new chock tube, I was in the setting position and it took me by surprise and just about put me on my back. The i shot some Hevi shot #6 and not near the recoil the Mag. blend had.