Fillers were at one time seen to be the solution to cast and reduced load finickiness.

Then maybe 20 years ago, reports indicating ringed barrels etc surfaced with enough regularity that the use of fillers of any kind were commonly discouraged in the gun press. I ceased using them for my purposes and I know many others did also.

Having read of enough troubles caused by the use of fillers I won't use them, but it seems there are some folks on this Forum that continue to use them and so far I have not read of any reports of damage coming from them. Maybe those who use them can weigh in and give their experiences.