Use a ball powder and you're fine. I've had good success with AA2230 and H335... both meter +/- .1 grain.
I tried Varget, and the best I could get was +/-.5 grain - not good enough in my books!
I've loaded thousands of .223 with my 550 and never had a single issue. The machine, once set up properly, will run like a top and create consistent and accurate loads!