Making the dies:
Use a Lee 221 Fireball dies. Counter drill .404 dia. to shoulder and no deeper (straight wall no taper you are making a neck sizer) Br very careful not to damage the shoulder. Face off die so length from shoulder to shell holder is .612 or slightly longer. Now face off seater die so length of shell plus shell holder engages the crimp shoulder.
1) cut of .223 rem case to 1.075 with tubing cutter and chamfer case inside and out.
2) Anneal 3/8" of the case mouth
3) Use Imperial sizing die wax for lube
4) Full length re size cut off case in a 22 jet full length re sizer all the way to the shell holder
5) Full length size to form shoulder and case neck in the modified 221 fireball die. the case should now start to look like a 22 TCM. Case neck after forming is around .018 thick trim to length (1.025) outside turn neck to .015 (.012 min .015 max)case should fall into chamber easily. load and fire form. max oal length 1.257 to fit magazine. use 225107 cast boolit on top of 9.1 grains of accurate #7 i used a rem small rifle primer.