Makes me think about how that sometimes powders have sweet spots as to when they burn all the powder. Thinking of 4227, in particular. You have to start getting near the max load in some cases, for all the powder to burn and cases can sometimes clear up somewhat.
I did think about a jacketed bullet, ( just to try for grins and giggles ), but alas no data for them on the Alliance website.
You didn't state load data but maybe you can possibly step it up and burn more of the powder and reduce the residue.