I have loaded many thousands of cartridges,over the years,with fillers.
First,I used Cream of Wheat cereal;then some other cereals;then Kapok;then Dacron. Dacron is my favorite.
Recently,some Folks report damage to guns because of the Dacron. I have become 'gunshy',and no longer make loads that have less then 50% powder in them. I still have confidence in my loads of greater powder charges,as long as I am sure that the filler is firmly on top of the powder.
Any gap between the powder and the filler will destroy accuracy,and may do worse.
Some more advanced shooters suggest that pure cotton be used instead of Dacron. The theory being that natural is better then synthetic. If you are a little leery,I suggest that you use cotton balls.
I bought a bag of those balls,myself,and wil try them the next time I load up some 45/70 ammo.
Frank