I'm not 100 percent Certain, so I'm just going to ask, are you wanting to shoot a actual 17-223? Or just neck down 223 cases to 17 Rem? you can do that, however the case is about .035 shorter which is not a terribly big deal, just means you may never have to trim a case, im a big fan of the 17 Rem, I have had at least one if not two in my possession since 1979, I've taken around 300 coyotes using one, at max velocity using a 25gr bullet sighted 1.5 high at 100 yards its 1.5 low at 300 yds, RCBS makes or at least they did back in the 70,s a single die that would allow you to bump the should back, then a pass thru a full length sizing die and one was ready to load and shoot, depending on chamber dimensions case necks may need to be turned, my first 17 was a Rem 700, I formed a couple hundred 223 cases and shot them in that rifle with no problems or accuracy change between case's I latter decided I should have a 17 on the little sako action which quickly became a favorite rifle,