Let me know how your workup goes. I would suspect at 75grs you may be filling the case to full capacity. I guess it will depend on the consistancy of the Magpro compared to RL19. I'm workinga load for my .300wsmusing 70.5of RL19 with a 168 Barnes TSX andits definitely a compressed load. According to the Barnes manual 71grs is max. Of course the Barnes are on the long side some what too.

Goodluck with your workup and keep me posted