Whenever the term 'corrosive ammo' gets tossed around new shooters, most of them recoil like a vampire exposed to sunlight. They think that shooting corrosive ammunition is akin to dumping highly concentrated sulfuric acid down the bores of their handguns or rifles.

This couldn't be further from the truth.

Although using corrosive ammo will corrode and pit the internals and barrel of your firearm, you can comfortably shoot corrosive surplus ammunition so long as you follow the proper cleaning procedures that we will outline in this article.

I hope you bought a can opener for that spam can of military surplus ammo because we are going to pull the trigger on some corrosive ammo and learn what it is, what it isn't, and how to ensure your firearm is clean and protected from corrosive ammunition.

What is Corrosive Ammo?

Corrosive ammo is a bit of a misnomer as the ammo itself is not corrosive, however, the primers in this ammo contain a priming compound that utilizes corrosive salts. Once fired, these corrosive salts will be deposited in the barrel, gas system, bolt, and chamber of your firearm and begin to corrode unless properly and quickly removed.

How can you tell if ammo is corrosive?

Unless stated on the ammo container, all military surplus ammo that is Berdan primed should be assumed to be corrosive, while Boxer primed ammo will be non-corrosive.

To understand how corrosive primers came about, it's a good idea to take a quick look at how centerfire cartridges, primers, and primer chemistry evolved over the years.

Evolution of Corrosive Primers

Between 1808 and 1812, the Swiss gunsmith Jean Samuel Pauley created the first centerfire cartridge which utilized a percussion cap as the primer. A percussion cap utilizes mercury fulminate as the priming compound as it is very effective at igniting black powder.

Although mercury fulminate excels at igniting black powder, smokeless powder exposed the shortcomings of the percussion cap.

Mercury fulminate will slowly decompose over time, meaning that eventually, the percussion cap will lack the energy required to ignite the smokeless powder. This was never realized as an issue with black powder, as black powder is so combustible that even static electricity can ignite it.

The next evolution of priming compound was adding potassium chlorate to the mercury fulminate to stabilize the mixture. However, this evolution presented new problems.

Higher pressure smokeless powder rounds would leave mercury deposits inside the barrel and the brass cartridge case. The mercury coating would embed itself into the brass, therefore weakening it and making reloading impossible.

The US Military decided to stop the use of mercury-based primers in 1898 and began working on a new primer system. Frankford Arsenal proposed the FA-70 primer that utilized potassium chlorate as an oxidizer for lead thiocyanate.

The FA-70 Primer is corrosive and here's why:

Once fired, potassium chlorate or sodium perchlorate primers will deposit corrosive salts into the barrel and internals of the firearm. These corrosive salts are potassium chloride and sodium chloride.

For all the chemistry savvy readers, you'll note that sodium chloride is table salt.

Now, neither of these salts are corrosive on their own…I mean you wouldn't think that you're adding corrosive material to your favorite cut of meat at the dinner table!

However, potassium chloride and sodium chloride are hygroscopic. That's a fancy chemistry word that means they will attract water from humidity in the atmosphere. Once combined with water, the corrosive salts will begin to corrode anything with which it comes into contact (think of how saltwater quickly rusts exposed metals).

For US Military surplus ammo, most of what is available will be non-corrosive. However, there are some lots that you might find in the wild that are older and have corrosive primers.

Any military surplus ammo bearing these headstamps (located around the primer pocket) or earlier will be corrosive:

.45 ACP: FA 54, FCC 53, RA 52, TW 53, WCC 52, WRA 54
.30-06 Springfield: FA 56, LC 52, RA 51, SL 52, TW 52, WCC 51, WRA 54, FN 57

Any surplus you find with those headstamps that has a higher date will be boxer primed and non-corrosive.However, Russian and Yugo military surplus ammo is the most common corrosive ammo on the market. So how do you tell if this Comm Bloc ammo is corrosive or not?

A good rule of thumb is that if it comes in a spam can, it's corrosive – for example, Yugo M67 ball, which some shooters describe as "mildly corrosive."

Gone unchecked and uncleaned, corrosion will set in and invite a host of additional firearm problems regardless of how "mildly corrosive" an ammo lot is.

All modern Russian produced ammo (e.g. 7.62x39mm, 5.45x39mm, 7.62x54R) will be Berdan primed but will be non-corrosive. It should say so on the box.

What happens if you do shoot corrosive ammo in your firearm? Is your prized rifle or handgun doomed to a life in the rust bucket?

Not at all! There's a cleaning procedure that, if you follow, will remove the corrosive salts from your firearm.

For tips on how to clean corrosive ammo continue reading here.