As I read more about loading 223, it seems that one is well advised to check case dimensions after sizing. Which tool is best. I have a lot of range pickups coming from mostly AR's.

I pick up 223 brass and use it. I don't bother measuring. I sort by headstamp and set them aside until I can process, size, and prep and a few. Then I run the empty prepped case into a chamber. My die setting allows for slight resistance on bolt close. If a few cases from a batch act politely, I process and size the rest and put them with others of the same make/headstamp. If they don't, and I have a bunch of them, I will play with the die setting and see if I can size them to fit well. If I can, I do, and they get loaded at some point.

I have some RCBS dies that size the bases smaller than the usual Lee sets I use. For stubborn cases, as a last resort, I run them through the RCBS sizing die. If that doesn't produce satisfactory results, the cases go into the recycling.

Citori16,
Wilsons makes "case checker gauges" to do what you want.
You simply install a case in the bottom and you can see where it falls between maximum and minimum SAAMI specs for a cartridge chamber. Then you can set your dies to resize your brass where you want within max. or minimum.
Most places that sell reloading equipment sell them.
IIRC the last One I bought I got from Sinclair.
Good luck,
-Ted

If ya don't like fiddling with things a Wilson case gage works fine. Just drop a case in and visually check. I buy an RCBS case mic for every caliber I load for! I can't imagine loading without one!

your chamber is the best gauge. If it slides in and there is a little resistance to bolt closing, then load em up and form to your chamber. Or you can FL resize find no resistance then fire form. Don't make it hard on yourself.

And then neck size after forming.

Yup.