Citric acid, probably available in every grocery store right now as canning season is here. It will look like very fine sugar in the bag.
And unlike ammonia, it does not weaken the brass. Nor are you going to end up with some sort of solution that will poison everyone, damage pipes or septic fields if you dump the used solution down the sink, etc.
Mix 1 or 2 teaspoons citric acid per quart water. That's 8 teaspoons per gallon. Since 1 tablespoon equals 3 teaspoons, you should to mix 3 tablespoons citric per gallon water to equal the recommended solution strength.
Use hot water and your range brass should look a lot better. With hot water, the brass cleaning happens almost instantly. Not only will it clean the corrosion and grunge, but it will passivate the exposed surfaces of the brass. This means they should remain shiny without further corrosion beginning for a long, long time. Citric acid passivation also helps prevent stress corrosion cracking in brass-- so if one reloads/stores OLD brass for obsolete calibers, the citric acid wash could be beneficial there too.
Citric acid will also passivate stainless steel and copper. A 10% solution at 140* will passivate stainless steel tools/parts in one hour. I use citric acid to passivate stainless tools that will be used in a marine environment. Citric acid is also a very powerful rust remover. Soak rusty steel tools in a hot 10% solution and the rust will be removed and dissolved.
