Cheatermk3:
I fire formed First, but I didn;t use bullet;s!! Let me explain.
Make sure the .222 mag. case's will chamber in your gun.
Deprime with a depriming die. Reprime.
Use 5-8 gr. of a pistol powder. I used 8 gr. of clay's.
With a funnel put some cream of wheat in case. Compress that with a punch or a drill bit. Do this 2-3 time's until almost full. Fill last little bit with crisco. SHOOT OUTSIDE!!!!!
One problem I had doing this was I ruined 1/2 my case's. Primer pocket's expanded. A lot!! Next time I'll just use bullet's.
To do this, back your .204 die out so as to size about 1/2 of neck to 204 dia. Load as normal and shoot to fire form.
Hope this isn't to confusing???