Sorry for the delay, gentleman, but concerning shooting brass after shooting steel...
These guys do a better job of explaining it through a test here:
http://www.theboxotruth.com/docs/edu18.htm
What I have read from many sources has led me to have a strong belief that steel cases don't expand as much as brass cases do in the chamber, therefore, steel cased ammo will leave more powder and residue in the chamber than a brass case (which, by design, seals the chamber almost completely). Many people have had problems shooting steel cased stuff, then without reaming the chamber out, start shooting brass and have extraction failures. I'm no expert, but I certainly will stay away from doing so. If you have done it and you didn't have any problems, then honestly I'm sure you're fine.