Allbrian, I think RCBS has some videos on their website, or links to youtube for official, correct, how to do it instructions.
When you resize a typical shouldered rifle case, the expander ball goes inside the case before you resize.. The neck is typically sized small, and then as you withdraw the expander ball, the inside of the case neck is expanded to slightly less than bullet diameter. This provides neck tension, holding the bullet in place as it is lugged around in boxes, pockets magazines and the like, and keeps it in place when the cartridge is chambered. It also provides consistent "Bullet Pull" to retard gas expansion, creating the progressive burn necessary to generate pressure.
Someone above asked if you chamfered the inside of the case mouth. One step in case preparation - first time reload, and any time after trimming - is to use a chamfering tool to cut a slight bevel on the inside of the case mouth, easing the start of the seating process. Just a slight bevel, barely visible is sufficient. Still, I find I have to steady each bullet until it is inside the seating die.
You do NOT bell, or flare the mouth of a shouldered cartridge. Well, I suppose you could if you were loading cast bullets, but if using normal jacketed bullets, or gas checks on cast bullets, there is no need. Seat 'em one at a time, even in a progressive loader, and guide them into the bottom of the seating die.
