Jokerxx,
Both of the above are correct, IME. Bart is describing sizing dies set up so they let you size without using an expander. Expanders are known to pull necks off axis which is the biggest and most common cause of cartridge runout. Such runout can cause some chambers to let groups open up as much as an moa, while other chambers seem almost immune to it. That's an example of what Wncchester meant by nothing being automatic. We don't know whether your particular chamber cares about this or not. You have to learn that.
Runout is also one of those things where there are several ways to skin the cat. An economy approach is to use the Lee Collet die to size the necks and a Redding Body Die to size the rest of the case separately. That makes it a two-step process, but the cost of the dies, by the time you've bought several different neck bushings to cover different makes of brass, is about half. The Collet Die sizes all brass neck thickness to the same ID without adjustment, plus it won't ever allow an internal donut to form.
This video shows the Collet Die compared to a die with an expander, and you can see the difference in neck runout produced. The same will be true for the Redding dies Bart describes when used without an expander (usually you just put a next smaller expander in its place or lap down the OD of the built-in one). The collet die takes getting used to, and I like to lap mine lightly for smoother operation. They will not work in a progressive press, though, where the Redding and Forster bushing dies will.
Once you've got a case with a straight neck, there are two things you can do to insure the bullet goes in straight. The expensive one is to use the Redding Competition Seater Die (
comparison to a few others here). Forster also makes a sliding sleeve type seater. Forster has a less expensive version of theirs, but Redding's has a floating seater stem while the Forster does not, and which some feel helps keep things straighter in some instances.
The cheaper thing you can do to keep bullets straight is to buy a Lyman M die and flare the case neck just enough to get the little step in the neck that it makes to let you start the bullet in straight with a standard seating die. In this instance I would use the RCBS standard seating die as the long skinny rod that holds it's seating stem ram has enough flex that it acts like a floating seating stem, and it has a crimp shoulder. You would set that shoulder just far enough down to iron the Lyman step back out. Or you could use a separate .223 taper crimp die to iron the step out a little more gracefully and to make the exact case lengths less critical. Otherwise, I would use the Lee Dead Length Seater, which actually has a floating ram, followed by a .223 taper crimp die. I expect you might be able to set the Lee factory crimp die up to just iron the step out, too, but I've never tried it. Beyond the minimum crimp needed to iron the step out of the case mouth, I would not crimp an accuracy load further. Be aware this approach will shorten brass life if you don't anneal the case necks regularly.
One thing that's bound to occur to you along the way is that when a bullet feeds in a self-loader, that's going to tent to bend bullets off-axis. So why would all this straightening matter anyway? It turns out in experiments by A. A. Abbatiello and Harold Vaughn, that if the same amount of off-axis tilt is always oriented in the same direction in the chamber, it shoots as tightly as if there were no tilt. So you are relying on that loading ramp to bend them all the same way and for the direction to end up the same in the chamber each time. The downside is that if you have to eject a live round for a cease-fire at a match, you don't want to chamber it again, as you may now have two different tilts combined in an unpredictable way. You need to set such rounds aside for practice unless you know your gun doesn't care about this.