Forming .222 Mag from .204 Ruger involves setting the shoulder back and altering the shoulder angle.  I'm sure it can be done, but might not worth the trouble vs. buying ready made brass.   

Did you try the .204 brass? Wondering if they expanded ok?

You can make them out of the much more common .223. They come up a hair short but unless your trying to load a very short bullet out to the rifling on a long throated barrel you should be alright.

You need to taper expand the neck out. You'll have a double shoulder until you fire form them.

jim

I know that you have to anneal to make the brass more flexible, but at what point does one do that step?

In general it's best to anneal the case after you reform it since your cold working areas of the brass that weren't in some cases previously factory  annealed in the past.  This is especially important when reforming cases like .223 to 7.62 x 25 where you cut the entire shoulder off the case and reform a new shoulder and necks altogether.

I use a 650 degree Tempilstik http://www.tempil.com/products/tempilstik-original/ you can find them at most any place that sells plumbing and welding supplies,price ranges from $9 to $15 depending on the supplier but they go along way.  I usually mark my cases about 1/4" below the shoulder and when they reach the desired temp the tempstik material liquefies.

In general it depends on what parent case you have and what your converting it to as to the steps,some conversions are more involved than others but 270 or 30-06  is more commonly use brass  for 8 x 57 conversions.  I would probably convert the 270 brass once fire so as not to resize and then expand the neck any more than necessary.  The steps you posted should be fine for the conversion you want.