The Lyman Brenneke loads might be of use.

The crimper appears to be doing a perfect job. I have never been one for undersized slugs in a large bore, ie: sabots shooting .45 and .50 cal bullets. That would be like shooting .30 cal bullets in a .45 cal rifle.

I have rifles in small calibres. If I want to shoot game with a 12 gauge rifle, by jingy, it will be shooting a 12 bore bullet or ball. The only saboted slug I would entertain for a 12 bore rifle, woudl be the Lyman sabot slug which measures .690" (14 bore) give or take a couple thou.