Shadow, while you are correct about the dangers of ammonia, citric acid does not have similar deleterious effects with yellow brass (cartridge brass). Ammonia does significantly weaken brass and should not be used near brass cases. For this reason, Windex should not be used near cases.
Citric acid does not actually etch or dissolve the brass, it works as a reducing agent. It works only on the surface of the brass, taking the oxidized layer (corrosion) and reduces it back to brass. Theoretically you could leave the brass indefinitely in the solution and it would not be harmed. It will also protect the brass from future corrosion.
Additionally, I just did some more research and it appears that this wash should also be safe with Nickel cases. Citric acid reacts very strongly with iron, but not with nickel or chromium. This is why citric acid is often used to passivate stainless steel to protect against corrosion.
Hope this makes sense.