I had to use the dacron back when I had my .450 no.2 NE double. I can't remember the grains of dacron it took, I guess I still have it written down somewhere, but it's just enough to not have airspace. You definitely do not want airspace between a filler and a bullet. That's where dacron comes in, as it expands fluffy. Never had a single problem after years of shooting it with it's load of RL-15. A pleasant cartridge to shoot and low pressure compared to the others.