Chris,
I also used .223 brass to make my .25-21 when I owned a Stevens 47 in that cartridge. And I found turning down the web first was the only way I could get the .223 brass to form down and work. I tried turning various amounts of until it formed down, and then cut the case in half lengthwise to see how thin the web was before doing more.
After shooting a lot of the reformed and turned .223 brass in my Stevens I never lost a single case, and considered it a success.