Hi, long time competitive Service Rifle shooter with 223.
A couple of things. You do not need a small base die set for 223. But you will need to raise the ram so the shell holder touches the bottom of the die. Lower the Ram and turn the size die another 1/4 to 1/2 turn and lock it. If you raise the ram again all the way up you will feel "cam over" to get the ram all the way up. Be sure to lube the case, then size the case. You will not have quite as much cam over when the ram is at the top when sizing the case.
Cartridge gauge....I randomly grab a sized case, (lube cleaned off) and check to see if the case will chamber and eject easily. I drop an empty case in the chamber and close the bolt. The bolt won’t close on a case that is not sized correctly. The case won’t eject easily if not sized correctly.
If using GI brass you must remove the primer crimp. I like the Dillon Super Swag as it goes fast and I like the feel of a swaged pocket over a cut one when priming.
Best money spent for creating accurate ammo with GI brass is a primer pocket uniformer.
Get a good set of calipers and for trimming I like the Forster. Easy to set up and trimming goes pretty fast.
I shoot Sierra Match Kings which don’t have a crimp groove and I subsequently don’t crimp the rounds. I use neck tension only to hold the bullet. To ensure good neck tension I use a Redding Bushing die with the bushing sized for GI brass thickness. (works OK for other brass though too)
I would be willing to bet my twist rate is a bit faster than yours but for light bullets I find 748 gives me good results and foor the heavies, 77 and 80 gr SMK’s Reloder 15 is my fav. Varget does OK too. Varget does really good with 55 gr. FMJ’s. For primers I use Rem 7 ½’s or CCI BR’s.
Oh, and be sure to wrute down everything you do. This way you won't try something that did not work over again. Good luck, Tim