Brass used with smokeless powder, Strat-o-sheen & water for 45 minutes. No stainless steel pins. Tumbler is a converted cement mixer from Harbor Freight - batch size ~ 1000 pcs.
Brass used with Goex, first step is a drop of Dawn liquid detergent, 1/4 tsp Lemishine & water with stainless steel pins for 15 minutes. This removes all the crud from the brass. Rinse 3 times, then Strat-o-sheen & water with stainless steel pins for 45 minutes. Tumbler is a Thumler's - batch size 120-150 pcs.
I do not decap my brass before tumbling. I get excellent results in both cases. YMMV.
Holler