I have never tried to clean or polish cartridge cases as I strongly believe that the natural discolouration process of brass cannot be interfered with and ‘natural’ looks best. However I do clean the ‘bullet’ part of the round as I like my cartridges to have that ‘just out of the box’ look. I’m sure some of you are already thinking disapproving thoughts but please give this a go - it does work!
Metal polishes, abrasives and most other methods leave a horrible unnatural shiny finish and will by their nature remove an amount of the metal from the surface and they’ll also damage any painted marking on the bullet.
For years I have been using a solution of Ammonium Chloride in hot water and dipping the bullets into this solution until the natural ‘pink’ copper colour returns. It is also known as Killed Spirits and is available to engineers as a metal soldering flux.
Use a small container - an egg cup is about the right size - mix a small teaspoon of the powder into enough boiling water to almost fill the egg cup. Dip the bullet into the solution to it’s casemouth for 2 or 3 seconds and then wipe dry with a tissue. This first dip will remove any grease and dirt residue from the bullet and will allow it to colour up evenly. Give it a second dip of about 5 seconds and you will see the bullet lightening in colour. Dry it and give it another dip if required. You can repeat this process as often as is necessary to achieve a natural looking colour. You must keep the solution hot to keep it effective and I reheat it in a microwave every few minutes if I’m cleaning a lot of bullets.
When you are happy with the bullet colour wash the round under hot water to remove any trace of the chemical and dry it.
I then spray my rounds with a silicone lubricant which is effectively a very thin oil - dries quickly to a completely invisible film - but prevents those annoying fingerprint marks that can stain cartridges when they’re handled.
I have never had any problems with this chemical dip other than on the 8mm Lebel with it’s bronze bullets. These turn black! It does not affect any bullet markings that I have come across.
The pictures show a .303 Incendiary and a 5.56mm from my scrap box and which have been dipped just a couple of times but leaving the lower part of the bullet in it’s original colour to show the difference.