I can't recall where I read it at the moment, but I did hear of a fellow who was shooting full house .223 with plain base cast. I believe they were obscenely hard and bordered on frangible, but he was able to do it.
Another that I've read about with .223 was over on another forum. If you search cast lead .223 in google it should bring up some stuff to read. I won't give out the forum since this site is funded by hardworking folks that make cast bullets for a living. I'll let you do the searching on that.
Assuming it isn't much different than the 30-'06 I've shot with cast, I can offer that a gas check is helpful and I haven't had much success beyond about 2500 fps (I start to lose accuracy quickly above that number). Also using alox lube seems to be the best I've used for higher velocities.