Working on forming some 221 fireball out of 223 cases.
Round one -- Formed directly without a forming die on the first round. Using only a FL die minus the decaping/expander rod. Could get the brass to look good size wise on the exterior of the case. The neck was to small to insert the expander rod into it to size the inner section of the neck. This is where I stopped. I do not have a inside neck cutting tool.
Round two -- Used a forming die #1. FL sized, cut and trimmed one last step in the FL die with decapping pin in. Works perfectly to get .221 fireball brass.
Time to anneal, prime, powder and seat a bullet to go shoot.

The only step I am do different is the forming die. How/Why is the brass responding in such a different way with only one small step in there?

The forming or trim die has a slightly larger neck ID.

If you can cut off you brass before you FL size it you will not need the forming/trim die.

If you form the case with the FL die you can force the case mouth open with a lyman M die to get the right case mouth diameter.

Just be sure that your formed case necks are not too large for the neck of your chamber - when they are loaded.

Interesting.

I have one .221FB and another on-order, and just spent almost $400 on a thousand rounds of RP brass, which is not of high quality as too many necks split after one firing.

What brass did you use, and do you know the water capacity in grains of your new cases?