I can do it for you if Wayne doesn't have something for you. I usually use a wilson trimmer case holder, put a fired round in the holder and then into the lathe a drill it under sized. I then finish bore it to tap drill size and run the tap in. Unfortunately I don't have a wilson 223 improved holder but I'm sure I can figure something out

. Like I said if Wayne can't help you out send me a couple of fired cases in a padded envelope with a prepaid envelope inside so I can return it to you.
Oh I forgot, I am making an order with sinclair in the morning so let me now and I will by a holder to do it.