Captain E: Brasso a nono for just that reason. The ammonia makes the brass very brittle. It is a chemical reaction and I don't know the actual particulars but it is widely known that ammonia makes brass brittle. It doesn't matter on a belt buckle, but it does matter on a high pressure rifle or pistol case.
Since you are just experimenting with a few cases it is not the end of the world. Just scrap them and start over. Don't even think about reloading them. Believe me there are plenty more out there laying on the ground. Very seldom do I go to my range that I can't pick up 100+.223 cases or assorted pistol cases like .45's or .40's. Most people who shoot don't reload. Too bad for them. I very seldom shoot a factory load, and I have several guns which have never had a factory load fired in them.
The Petco walnut hulls are ground to a consistant size and used for Lizard or Snake bedding. Go figure.?
The Dillon Case Polish I recommended doesn't have any ammonia in it and works really well. It's about $10 a bottle. Get some of their case lube as well as it works really well too.
Learning to reload ammo is a very satisfying hobby. If you start out slow with maybe a Lee Classic Loader and a plastic mallet you will learn the purpose of every operation. All reloading whether rifle shotgun or pistol has the same basic steps. For each type of round there may be some slightly different steps in the process but "esssentially" all ammo is loaded using the same basic steps.
You deprime and size the case, you install a new primer, charge the case, put a bullet in, and crimp it in place.
The tumbling part comes under the heading of "Case Preperation." And there are a few other things to do in that area.
All of this is covered in detail in the Lyman 49 Loading Manual I suggested above. You can get one at just about any gun shop or big bookstore or Midway USA, Cabelas etc. @$30.
It will answer pretty much all of your questions and will serve as a referrence, and source for loading recipies for just about every cartridge known to man.
Lots to learn here and lots to know. The benefits are being able to custom taylor a load for any specific gun, improve accuracy, save money, produce ammo you can't buy anymore, and just the pride of accomplishment.
Randy