Upon getting more info on Brasso and its component ammonium hydroxide I am convinced that it would be "death for brass cartridge cases"
I have been told this:
Brasso contains ammonium hydroxide, NH4OH, a weak basic agent - ph greater than 7, in fact, it is used to detect copper solutions by making deep blue coloration, is a corrosive chemical as identified in the MSDS, creates a non-neutral ph on metal surfaces (bad), and attacks copper, aluminum, and zinc to such a degree these metals cannot be used to contain it.
Belt buckles yes, cartridge brass no