I have not seen any cost savings in reloading 223/5.56 ammunition for the prices you can get it on sale. If you reload with 55gr it cost as much or more than factory run. When you get into the 70+gr you might see a $0.05 savings, but I don't calculate the brass cleaning or time into my reloads. So if you are shooting a 1.5MOA with 55gr factory loads, I would just go with them. As for using a .223 die for 5.56 reloads, I have doubts. The 5.56 cartridge measures .218. I sometimes think this is what is causing my AR jams. I check all casings after firing for tolerance with a micrometer to make certain that they are in the specs, except the diameter of the shell after resizing. So with the trouble I've had reloading the 5.56, my .223 die will simply remain on the shelf. Now a comment on your question, I'm shooting a 1.0MOA at 200yds with my Ruger 5.56MPR using 55gr ammo. Looking at switching to 70gr after I use these up.