I do use filler, a product call Puff-Lon. I'm sitting at my loading bench loading 500 grain RN's in .458 WM using 56.0 grains of H4895 and then topping the case to the base of the bullet seating with Puff-Lon. Hodgdon has the 60% formula for reduced loads with H4895, but I have tested H4895 loads with and without filler and found better consistency with filler. It is cheap and easy to do, so why not. If there is extra space in a case, I am inclined to use filler to retain a consistent shape of the powder column... I'd far rather use filler than having to do a salsa dance with my rifle before every shot.