Jack,
I've fired volumes of the .225"-60g SPGC bullets out of my various .223's. They are great fun, and great predator harvesters if you are hide hunting. My load is this:
.225"-60g SPGC/10.0g Unique/Remington 7 1/2 Bench Rest primers/Federal Brass/2340 fps.
No this isn't a barn burner load for velocity, but I'll tell you what, it will shoot into under a half an inch in two .223's that I own. The others will group them into about an inch and a quarter. The key is to seat the bullet to just engage the lands of the throat for best accuracy results.
I have had mixed results shooting these and other powder combinations in the Ruger Mini 14 with cast bullets. Although accuracy has been good to excellent (for a mini) with cast bullets, there has been an issue of lead deposited in the gas port. I've found that the tip cleaners sold for use in oxy-acetylene torches work superbly for removing the lead from gas ports on many gas operated semi-autos. Not a real big deal unless you are working with a glass bedded national match Garand or something on that order.
Cast in .223's are great fun!
God Bless,
Marshall