I agree with reducing the charge based on smaller case capacity and smaller caliber but where to start. 5 gr, 3 gr. ???I am not sure how my gunsmith came up with the 10gr of Bullseye charge weight with the cornmeal. He built a lot of custom rifles, many for wildcat cartridges, so it must be from experience. I just know the 10gr charge of Bullseye works well on the 30-06 to 35 Whelen AI fireform. I think Ribbonstone's advice is sound on reducing the charge for your smaller case, and incrementaly increase until you get the proper case fill out of the chamber.
Just me, but I'd not fire a small bullet down a larger bore. Who knows what might happen? Call me a sissy, but that's where I stand...I have only seen one or two references on firing loaded 30-06 rounds in the 35 Whelen. Sure, the bullet will rattle down the bore but if the mess is lower, that might be a good thing. Any thoughts on this?