40 Grain V Max- 27.5 grains of Varget.
Varget is, in my opinion, the very best powder for the .223 REM.
It is the most accurate powder in all of my (3) .223 chambered rifles with a variety of bullets. Plus, it is in Hodgdon's "Extreme" line of powder so it's not temperature sensitive.
ETA: This is a hot load, so reduce it by 10% and work up to it.
You might want to pick up a couple of reloading manuals. It's really not a good idea to take reloading data straight off of a web site like this without verifying it with a good manual.