Corrosive Ammunition: Don’t Ruin a Good Gun

Two old ammunition boxes marked as corrosive ammunition

Any discussion of centerfire ammunition must start with development of the percussion lock. That is, after all, where the idea of a shock-sensitive substance to initiate the process was formulated. Fulminate of mercury was originally used as the priming compound, and striking it with a hammer was the method.

The primer substance was later changed to potassium chlorate. The Rev. Alexander Forsyth was the inventor that first used fulminates of mercury to set off the main charge. Fulminated mercury continued to be used in priming caps for early centerfire cartridges until the end of the 19th century.

1917 Artillery Luger barrel showing pitting from shooting corrosive ammunition
A 1917 Artillery Luger barrel after over 100 years. It was obviously shot in the field and not properly cleaned. It shows significant amounts of pitting and the effects of corrosive primers with just enough rifling to still shoot.

Proper Priming

As the transition to smokeless powder took hold, and people started to switch over, they began to discover the problems associated with using fulminate of mercury. This concept of using a shock sensitive priming material is still the state of the art in today’s centerfire cartridges. However, there were some issues with using such primer materials.

One of the most vexing issues was that fulminates of mercury tend to degrade when kept in storage. This was not a make-or-break issue when using them with black powder cartridges, because black powder ignites a lot easier than smokeless powders. However, once the transition to smokeless powders started, they found cartridges kept in storage for any period of time would cause the fulminate of mercury primers to degrade.

It degraded so much that it would not reliably ignite the smokeless powder. This caused misfires and hang fires. Another problem with fulminates of mercury was that when used with smokeless powders, it tended to form copper and zinc amalgams in the brass cases of cartridges. The amalgams made the cartridges unsuitable for reloading. It was primarily because of those issues that the U.S. Army switched from fulminates of mercury to using potassium chlorate primers in 1898.

Some of the primer manufacturers used sodium chlorate instead, and that opened another can of worms. While these primers did not degrade as much as fulminate of mercury, there were other problems that came with them. When fired, these primers would decompose and leave a residue of potassium chloride (or sodium chloride) in the barrel.

If you remember your chemistry lessons from high school, you might remember that sodium chloride is the scientific name for common salt. Potassium chloride is also another corrosive salt. These salts are also highly hygroscopic, which means they tend to attract water, especially in humid conditions.

Two old ammunition boxes marked as corrosive ammunition
Some of the corrosive ammunition is marked but there is a tremendous amount that is not. So, buyer beware.

Guess what happens when you have salt and water sitting on an iron or steel surface …Say the magic word and win a hundred dollars — Rust! Therefore, if the barrel and action are not cleaned after firing such cartridges, there’s a good chance that they will rust soon after. By the way, wiping the surfaces down with oil will not prevent these salts from attracting water and rusting the metal.

As a result, there was a push to develop primers using non-corrosive chemicals during the 1920s, but these were generally used in civilian ammunition only. The reason for that was because the early non-corrosive primers did not last as well in storage as corrosive primers and failed to satisfy the military’s requirements. As a result, military ammunition tended to use corrosive primers, and this was indeed the case for U.S. military ammunition until the mid 1950s or so.

Other countries (e.g. former Soviet Union, China, Yugoslavia, Bulgaria, etc.) continued to use corrosive primers in their cartridges for much longer, well into the 1970s and 1980s meaning that there are still large quantities of corrosive ammunition still out there. Therefore, depending on the source and the age of the ammunition, the user must be very wary lest they use corrosive ammunition.

Two old ammunition boxes without the corrosive ammunition markings
Two examples of boxes of ammunition that do not state if they are corrosive or not. Again, buyer beware.

M1 Carbine

As an interesting side note, it was one characteristic of .30 caliber M1 Carbine ammunition that from the beginning of production, non-corrosive primers were specified for its use. This was the first major use of this type of primer in a military firearm.

Because the rifle had a closed gas system, not normally disassembled in the field, corrosive primers would have led to a rapid deterioration of the function of the gas system. The use of non-corrosive primers was a novelty in service ammunition at this time. Some failures to fire were reported in early lots of .30 caliber Carbine ammunition, attributed to moisture ingress of the non-corrosive primer compound, and that is what led to the unsubstantiated stories of its lack of effectiveness.

Additionally, the .30 Carbine cartridge is essentially a rimless version of the obsolete .32 Winchester Self-Loading cartridge introduced for the Winchester Model 1905 rifle. The propellant was much newer, taking advantage of chemistry advances. As a result, the .30 Carbine cartridge is approximately 27% more powerful than its parent cartridge.

FN1949 rifle that had been the property of the Army of Luxemburg
The FN1949 that had been the property of the Army of Luxemburg. Which was the gun that I learned my lesson on how to deal with corrosive primers.

A standard .30 Carbine bullet weighs 110 grains and has a muzzle velocity of 1,990 ft/s giving it 967 ft-lbs. of energy, when fired from the M1 carbine’s 18-inch barrel. The carbine round is twice as powerful as the .45 ACP caliber Thompson submachine gun. As a result, the carbine offers much better range, accuracy, and penetration than those submachine guns.

The M1 is also half the weight of the Thompson and fires a lighter cartridge. Therefore, soldiers armed with the carbine can carry much more ammunition than those armed with a Thompson. As a consequence, the carbine falls somewhere between the submachine gun and assault rifle and could be called a precursor of the personal defense weapon, since it fulfilled that role so perfectly. Additionally, M1 Carbine buyers need not be as concerned about one having a pitted, shot-out barrel.

To ensure that a shooter does not suffer adverse effects in his firearm, and that it doesn’t rust after using corrosive ammunition, one must take appropriate action. The good news is that this is fairly easy to handle. It turns out that these corrosive salts dissolve in water. Therefore, cleaning the firearm thoroughly using water or a water based lubricant should do the trick.

The firearm should be thoroughly cleaned as soon as possible after firing the corrosive ammunition. This is done to ensure that the corrosive chemicals are removed before they can damage the firearm. I was taught the lesson to clean my firearms as soon as I got home on a FN1949 that had been the property of the Army of Luxembourg.

I was convinced to buy it by the salesman who told me it was the finest semi-auto rifle that was ever made. Its fit and finish had no peer, and I just had to have it. He also gave me two boxes of ‘06 to sweeten the deal. What he didn’t tell me was that it was corrosive from WWI.

I found that out when I took them to the range and was told to scrub the barrel, action, and bolt face with hot soapy water lest I damage my pristine prize. As soon as I got home, I bathed it and made it a practice to use hot soapy water when ever I suspected corrosive ammo was used. Others use plain water, still others swear by Windex glass cleaner (which is largely water based). After washing off the residue, the firearm is then dried, cleaned with normal bore cleaning solution and oiled, as per the normal cleaning procedures.

F A Headstamp on this cartridge indicates it was made in 1940 at the Frankford Arsenal, a former United States Army ammunition plant
The F A Headstamp on this cartridge indicates it was made in 1940 at the Frankford Arsenal, a former United States Army ammunition plant.

While this may seem like a lot of extra work, it is well worth it because there is no way to restore a barrel or chamber back to perfect condition — once it has started to rust. Anyone that suspects, even the slightest possibility exists that they may have fired ammunition with corrosive primers should go through the extra effort if any doubt is suspected the ammunition contained corrosive primers.

How to Determine

As it turns out, the price of surplus ammunition using corrosive primers is often much lower than other types and it is also widely available in the market. So, how can you identify whether the ammunition is corrosive or not?

One way is to look at the markings on the cartridges and the manufacturer of the ammunition. If it is surplus ammunition from certain countries such as the former Soviet Union, Yugoslavia, or China, there is a good chance it uses corrosive primers — especially if it is manufactured before the 1980s. U.S.-made ammunition has markings that can give a good clue as to whether the primers are corrosive or not.

Examine the head of the cartridge and look for the date of manufacture. If it is U.S.-made, and dates before the 1960s, it should be suspect. Anything foreign made, especially Russian or Chinese should always be suspect.

In case of doubt, there’s an easy way to find this out. Take a random cartridge, pull out the bullet from the front and empty out the powder from the cartridge and only leave the primer behind. Then, fire the empty cartridge onto a mild steel plate from a distance of about one inch from the muzzle, so that the primer chemicals are deposited on the plate.

Rifle bolt showing the effects of corrosive primer discharge around the firing pin hole by he deep pitting in the circular pattern
This bolt shows the effects of corrosive primer discharge around the firing pin hole by he deep pitting in the circular pattern.

Then, fire another primer that is known to be non-corrosive onto another section of the steel plate. After firing the two cartridges, clean the firearm as detailed in the procedure above, in case the suspect ammo is indeed corrosive. Next, simply keep the steel plate in a warm humid area for a few days. If the section where the suspect primer was fired shows substantial rusting, it uses corrosive chemicals.

Another way is to follow the same procedure as described above only use bright common nails (which are nails made of mild steel with no coating) and pop a primer over one of these nails. If the nail rusts within a couple of days, then the primer is corrosive. Something to watch out for today, we often find that a box of ammunition actually says that it is non-corrosive on the box, but it turns out that it, in fact is corrosive after all. Shoot those old antique firearms, but be sure to use correct methods of cleaning them to protect your investment.

Have you fired corrosive ammunition in the past? Do you have a horror or hero story as a result? Share your answers or tips for shooting corrosive ammunition in the comment section.

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (17)

  1. Very informative article. I always was unsure of the foreign ammo I have bought. That test would confirm it. I never cleaned my weapons after every use. This article would change the way I will handle my cleaning from this point forward..great information.

  2. What has always been and what will always be the absolute best cleaner is good old water. Black powder and corrosive primers are both hygroscopic. I’ve been using Hoppe’s #9 for decades, great product. Of course after cleaning with water(cold water) always Oil and yes, recheck in a couple of days.

  3. I bought a Mosin 91-30 circa 1943 when a 440 round can of surplus ammo was $60. I find Hoppes does well for cleaning. However, it is like cleaning a black powder rifle for the number of pads needed after shooting several rounds.

  4. Very informative information. Using the same phrase that many industries/tool makers/firearms enthusiasts/others use, “cleanliness is godliness”. I know that was the case in my line of work (metal working and welding).

  5. Hoppe’s #9 was developed FOR corrosive ammo. I shoot old military guns with lots of corrosive ammo. None show any ill effects. I do like to always check the guns a day or two later to re-check them. Do NOT reload the cases of corrosive ammo. They can have case separations.

  6. Shot my #4 Mk1 Enfield over 50 years ago with some surplus ammo. Cleaned and the bore looked good. Two days later and the bore was DARK as if I hadn’t touched. Cleaned again, checked a couple days later. Dark, but not as bad. Cleaned, checked again. Looked good, but I kept running oiled patches for a few days afterword. Since then if I shoot suspicious ammo. I follow up shooting a number of rounds with my non-corrosive reloads. I clean and check the next day. The bore is bright!

  7. I just bought 7.62 x 25 Tokarev ammo in 50 rd sandwich bags. Mixed cases and the ones I suspect, have a head stamp of 22 above 83 and instead of being cramped on the mouth they have three pinpoint crimps on the side of the neck. Other cases are PPU and don’t demonstrate any case mouth crimp, while even more cases have a black tarnish on about 30% of the case.

  8. I will not fire any suspect ammo in a gas operated semi-auto: too many nooks and crannies to clean properly. If I fire corrosive ammo in a bolt gun I scrub the barrel and bolt face with generic Windex “with ammonia” and rinse with 90% rubbing alcohol. I like alcohol rather than water because if I miss a spot when drying, the alcohol will surely evaporate. Follow up with generous application of good gun oil. Wait a couple hours and wipe off the excess oil. This has worked for me. It also has worked for my muzzlloaders, though I don’t use blackpowder. Stay safe.

  9. I have a Mini -14 also and if Chinese fighter planes fly low enough, corrosive or non corrosive ammo I hope I can penetrate and at least make sure that pilot has a bad day. It’s a shame I have to look up in the sky and worry if that aircraft is one of ours or not

  10. I’ve found Hoppe’s worked to remove primer salts, always check a day or two later. French military M1 carbine ammo is highly corrosive as is some marked FA but actually made in China.

  11. I got bitten by corrosive ammo in an Egyptian Hakim. I failed to clean it enough and suffered bore and chamber damage due to rust

  12. These days, most of the corrosive ammo that’s still in circulation is foreign military surplus. Even though my 1939 vintage Mosin-Nagant already had a pitted barrel when it came to me, after I fire Russian milsurp ammo through it I clean the bolt thoroughly and pour boiling water through the bore, since I assume the ammo is corrosive. (I finish cleaning in the normal manner.) As for my other guns, I make it a rule not to use ammo that’s older than I am (I’m retired) or ammo that comes from a country where I wouldn’t drink the water – that keeps most corrosive ammo away today.

    The article mentions a method of testing to determine whether a primer is corrosive by firing first a suspect primer at a metal plate, and then a known non-corrosive primer. The order should be reversed, fire the good primer first, and THEN the suspect primer. It tells you nothing to fire a good primer through a bore that MAY have already been contaminated by a corrosive primer.

  13. I learned about corrosive ammunition the hard way. I had never heard of this and my first gun – a Norinco SKS ended up with a rusty piston and barrel pitting
    Sad end for a great little plinker. I had numerous spam cases through it and it never stopped working but wasn’t pretty in the end. I wish i knew this years ago!
    Another great article by The Most Interesting Man. Keep ‘em coming!

  14. Just bought a new box of Winchester 223’s for my Mini 14 which obviously has corrosion free primer. Question for Mr. LaPorta is: Will it now reach 60,000 feet? There’s a big white thing floating around up there and quite frankly, it’s pissing me off! Another excellent article. Thanks!

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