Re: best 223 dies?
I did a long experiment on groups of brass, a handful of dies, and my [I guess I forget how many 223s I own].
I measured the headspace of each rifle. The factory rifles had a lot of heapspace. The ones I barreled have only about .001" over SAAMI min chamber. If ammo is shared between rifles, the long head space rifle stretch the brass, and the die must be adjusted down far enough so the ammo will fit in the short head space rifles. This makes brass grow fast.
What did it all teach me?
1) Hot loads and full length resizing to push back the shoulder far enough to fit in any of the rifles, results in fast case growth. One or two shots and they need trimming. When trimming must be done, for real, not per some manual, involves how far the firing pin can push the case forward in a particular rifle.
2) Redding "S" die cost the most, looked the best, and performed the worst.
3) Lee collet neck die cost the least, looked the worst, and performed the best.
4) Life is so much simpler if the brass stays with one rifle. The single shot rifles [not the ARs] can get 20 shots of WAY hot loads without trimming.