No. It is Improved not Ackley Improved, the 204 Ruger shoulder is moved forward so you would have excessive headspace if you used 222 Rem Mag brass without creating a false shoulder to headspace on. That's why I Capitalize IMPROVED to differentiate from Ackley Improved.
There were many different shooters Improving/wildcatting cartridges, Gibbs, Mashburn, Kilbourne, Gibson,Donaldson and the list goes on a long way, including myself(I built the first 25-204 the year 204 Brass became available, inspired by the 257 Kimber). Most did not create cartridges that the parent case could be simply fired in the improved chamber to form the new case.