A friend gave me a bunch of 9mm cases and, while they looked like they were brass, they were actually brass washed steel. The headstamps were CC and Xtreme. In my research, I have also found references to some SIG cases being brass washed steel but haven't actually seen any.
CC
Other products listed on their website include primers and bullets.
X-treme
X-treme cases are products of X-tremebullets.com
CC
CC
Capital Cartridge
From website: "Capital Cartridge has been supplying once-fired brass shell casings for commercial and recreational reloading since 2012." Their website features quantities of washed and polished fired cartridge cases of various headstamps both with and without the fired primers. The only cartridge cases with the headstamp of "CC" are sold new and unprimed on their website. Assembled Capital Cartridge handgun ammunition with CC headstamps are sold on their sister company's website (2A Warehouse). They feature both rifle and handgun calibers.Other products listed on their website include primers and bullets.
X-treme
X-treme cases are products of X-tremebullets.com