What is “corrosive” ammunition? Corrosive ammunition is ammunition that uses a primer that has chemicals that when ignited leave a residue of corrosive salts. Most often these primers have potassium chlorate, or sodium petrochlorate which, when burned, decompose into potassium chloride or sodium chloride. Sharp-eyed readers will note that sodium chloride is also known as common table salt.
Potassium chloride isn’t much different than common table salt, and both are very hygroscopic (meaning that they attract water) and, because of that, highly corrosive. We’ve all seen what salt water does to metal. The same thing happens to your rifle when it is left uncleaned after firing corrosive ammunition. Potassium chloride and sodium chloride are pretty harmless alkalis, but when exposed to the hydrogen and oxygen from the ambient humidity in the air they can form a powerful acid that will cause the steel in your rifle to rust and pit.
Most modern ammunition is not corrosive, but old military surplus ammo is different. For surplus ammunition, there are two main types of primers: Berdan and Boxer. Boxer-primed ammunition is not corrosive, so you don’t have to worry about it. Not all Berdan is corrosive, but almost all of the surplus ammunition you find on the market with Berdan primers is corrosive. If your ammunition is Berdan primed, it’s better to be safe than sorry and treat the ammunition as if it is corrosive. It won’t hurt your rifle to clean it, so it’s a good idea to thoroughly clean it to get any salts out any time you’re shooting Berdan primed ammunition.
In the past, when corrosive ammunition was standard issue for the military, soldiers would simply rinse the gun with hot soapy water. Since the corrosive salts are hydroscopic, they readily dissolve in the water. The basic solution of soap and water also neutralizes the acids created by the corrosive salts. The weapon would then be dried out and re-greased or lubricated.
The same method can be used today. First, you should always make sure that your firearm is unloaded and safe. Then, simply disassemble your rifle and immerse the parts small enough to fit in a basin of hot soapy water. For the barrel or other parts too large to fit, you can carefully rinse out the part by pouring the soapy water over it. Once the parts are removed, the hot water will quickly evaporate. WD-40 or some other water-displacement fluid can be used to make sure no water remains in little nooks or crannies in the rifle.
If the thought of soaking your precious rifle in soapy water doesn’t seem like something you’re comfortable with, you can use any aqueous solvent like Hoppes 9 Plus or Shooter’s Choice Aqua Clean. Both of these cleaners are water based and have solvents that will dissolve the corrosive salts. In addition, they will also work for general cleaning of your rifle as they will remove carbon fouling and buildup. Don’t forget to properly swab the bore with an oily patch, and oil and lubricate your firearm after cleaning.
Corrosive ammunition is perfectly fine to use. The corrosive surplus ammunition on the market is a great inexpensive way to enjoy your military rifle. By properly cleaning your rifle after using ammunition that is or is suspected to be corrosive, you can ensure that your rifle has a long and corrosion-free life.