Very easy to do.
First I resize in a 223 die without the expander ball.
Then I resize in a 17 rem die, the 223 case should be done slower than usual, I like to go up
into the die a little at a time and back out and then a little more until it's sized without
the expander ball. No excess lube on the neck, none on the shoulder or inside the case neck yet.
The neck will usually be a bit to thick and I trim them down most times about 002-004.
Most regular 223 cases will be fine but military cases always come out with a thicker neck.
Then I run them up in the .17 die again with the expander in and check the neck again after
the expander ball runs through. A few thou thicker chambers in my rifle, as long as it isn't tight.
You get a feel for how much pressure you can put against the
case when running up in the 17 die, you will get some dents in the shoulder esp. if you go about this to fast.
Most will blow out when fired, some don't if they are straight they are GTG. I use a grain less CFE223 or 4320 in theses cases from first firing on. The neck is a hair shorter, esp. with military cases, less with regular brass .I do not get a carbon ring in the chamber, I clean the barrel and chamber like always and can use regular 17 brass loads anytime.
The slower you push the 223 case up into the 17 die the better the shoulder and case neck will be. I shoot under 3/4" inch groups with these cases with Hornady 25gr V-max & 24gr 4320, 7 1/2 primer.