Just my opinion backed up with a few years experience Fillers not really needed with trailboss due to its volume, or with the "universal cast bullet loads" using from 4 to 10 or so grains of unique or shotgun powder. Consistent Ignition will occur regardless of the powders position and there's no detectable difference in velocity or accuracy.
Only place I do use filler is in BP cases when I'm "light loading" to 3/4 or less of the full charge. BP is a different beast, and in those situations I like to use felt or teased fleece.
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