Edwin, I've used the 55gr Lee bullet molds (2 different designs) in .223 Rem. One of them has a pretty blunt flat nose that seems well suited to short range accuracy but has some potential for feed issues in some guns. The other design is a longer flat nose that seems to work well enough. I used them with powder coating and cast them hard (heat treated); those could be pushed as fast as jacketed bullets with no concern of leading. However I found they were fairly sensitive to getting all the details just right compared to larger cast bullets or .224 jacketed bullets, so I haven't spent much more time on them.
If I were to tackle cast .224 bullets more seriously for high velocity use I'd use a design with no lube grooves, and powder coat them of course. I think some of the accuracy issues I encountered at high velocity were due to the grooves collapsing under pressure, but have not spent the time to confirm that.
