I just started casting for my AR 223 and so far is has worked quit well. I won't say it is possible for every gun because I have heard enough people say they can't get it to work, but I have also heard enough people say it works well enough for them so I figured I would give it a go.
My mold is made by NOE (custom mold maker from Utah) and it is a clone of an RCBS 225-55 My bullets come out right close to 225 and about 62 grains. I am using a home made lube called simple lube designed by a member of the castboolits forum. It really is quite simple Petroleum jelly beeswax, ATF, and 2Stroke oil.
225-55 is a widely used mold and seems to be fairly popular.
As was suggested above, visit the castboolits website and do some reading. They are good folks and will help you out quite a bit.
* (Swinging club) Whack! whack! whack! *
Nope, the old nag's still dead .