Maine Woods,
Good luck with loading your .223. I just started working on loads for the .223 Ultra. I started using military surplus ammo, 55 gr. just to sight in the gun and get it on paper at 50 yards. It shot a 7/8" group which isn't that great for the .223. I then shot my first string of Sierra 53 gr. reloads, and dropped the groups down to 7/16". A big difference, and with just my first run a loading for it. I have a lot of playing to do yet, but now I can move the range out to 100 yards. You'll find there is a lot of throat in these guns. I tried to get the loads to close in on the rifling, but the bullets will drop out of the brass before they'll touch the rifling. As it turns out, my concerns were unfounded.
Don