I had to laugh when you said "I am glad I only have to do it once."
Are you able to get decent accuracy with the 5.56 brass?
Yes, you can, but are you ready to trim and anneal and turn the necks??
Like I said, once you resize and prep the case (except for the case walls) you now have 223 brass. Just don't let the head stamp fool you.
My 223 bolt Savage has a 1:9 twist and the only bullet I use is the Hornady 75 grain A-Max. The rifle shoots them like laser bolts right to the target. Less than 1/2 MOA all the time.