This is from an old Ideal Handbook, No. 30 (1931), pg. 9. I tried my best to enter the text exactly as originally printed. I added the bolding on the parts I found to be most unbelievable, and funny.
"To clean cases which ave been fired with smokeless powder, first wash them in soapy water and rinse in clear water. Then immerse them for not more than three to five minutes in a solution of one per cent. sulfuric acid and water, which must be contained in a wooden tub, glass bowl or an earthenware vessel. Do not let them remain long in this, but remove and at once wash in several changes of clear water.
This leaves the cases clean, but they will probably be black which does no harm. The best way, however, to clean fired cases so they will be as bright an clean as when new, and with the least labor, is as follows: Procure two quart preserve jars or other large glass vessels. Fill No. 1 jar with 1 quart of water, 2 ounces of sulfuric acid, and 2 ounces of potassium bichromate. Fill No. 2 jar with 1 quart water and one-fourth pound of sodium cyanide.
Both these solutions are deadly poison, and if mixed will give off poisonous gasses. Arrange these these in the following order from left to right. No. 1 Jar - a kettle of clear water; No. 2 jar - another kettle of clear hot water. Take a piece of wire and bend in the form of a double hook with long handle in the middle. Hang two cases on the hooks, mouth down, and dip them first in No. 1 jar..."
Well I'm tired of typing but you get the idea, just go on down the line. Whew, we've certainly come a long way since then. I imagine if you even tried to by the chemicals it wouldn't be long before homeland security would be knocking on your door