So I've noticed one of the set's of dies I have from Lee has a powder through expanding die with it. I'm just curious as to what this does? I've never used it and am wondering if I need to be using it. So far what I've done is resize the case, charge it with my RCBS Chargemaster, then seat the bullet, and then run it through the Lee FCD. I've never used this powder through expanding die. Am I making a mistake?