The peening is caused by the cases striking the case mouth, therefore the more cases the better within reason. I have a standard Thumler's Tumbler Model B High Speed model with a 15 pound capacity and this tumbler is rubber lined. The LemiShine contains citric acid and cleans and adds shine and bling to the cases, the dish soap helps clean and also holds the dirt in suspension. Meaning if you do not use enough soap it takes longer to clean the cases (see note below in instructions)
http://www.stainlesstumblingmedia.com/thumler-s-tumbler-model-b-high-speed-7.html
Instructions for Thumler's Model B Tumbler
Notice. It takes a few times to get the media broke in. The media is dirty from manufacturing process and has a few burs. Media does not work in a vibratory cleaner
1. Add 5 Lbs (2.27 kg) of SS media into the drum
2. Next fill with 1 gallon (3.78 Liters) of cold water. (One gallon)=8 Lbs/3.63 kg
3. Add your brass into the drum (2 Lbs/907g of brass)
4. Add dish soap. 1 -2 Tbs (15-30 mL) of either Dawn, Ivory, or Joy dish soap
(if there are no soap bubbles in the water after you tumble, you need more soap)
5. Add 1/4 Tsp. (1.25 mL) of Lemishine. This is the key to the shine. (Not too much)
6. Tumble 3-4 hours with the Model B High Speed Thumler’s Tumbler
7. Pour out as much water as you can without losing any brass or pins
(The more you rinse the brass and pins the better your results will be next time)
8. Fill drum with water, and separate brass by hand or use an STM Media Separator with water.
9. Rinse your brass off really good with some warm water. (Not getting a good rinse can leave water spots on the brass)
10. Dump brass onto a towel and let dry. If any pins get stuck in the neck of the brass throw those pins away
11. Store Stainless Steel Media either wet or dry in drum