Here is how I ended up re forming 5.56mm to 222. First found this batch of about 350 All same lot Fed LC brass a couple nice young fellows gave me after they’d swept it up at the range In Effingham.
Tumble clean in corn cob media.
Anneal cases.
Lube with Dillon spray case lube. Wipe shoulder off with rag to prevent lube dents. That’s the big trick.
Turn FL 222 die out 1 ½ turns. Stroke press then turn die in 3/4 turn and repeat until fully sized. This done with de caper removed.
Use a WFT drill powered trimmer to cut off 1/16th inch excess neck. $70 at Sinclair. Little Crow Gun Works Worlds Finest Trimmer.
Anneal cases again.
Expand necks with Lyman M die.
Decap with Lee universal decap die.
Uniform flash holes.
Uniform primer pockets.
Chamfer pocket crimp out with Hornady reamer.
Tumble clean.
Finally a week later of all my spare time I’ve about 350 cases ready.
Most of that work you have to do to any mil surplus brass to get 223 out of.
The other 100 cases I have were real hard. Went onto Powder Valley online catalog. Clicked on Lapua 222 brass. Couple mouse clicks later and $50 they were at my door in three days. When brass is available you can buy 500 Remington’s for $155.
Neck wall thickness is a little thicker at the bottom where neck was formed from shoulder brass. But not so much there still isn’t plenty of room in my CZ even with a .225” boolet seated. About a fat .001” diameter.