Corrosive Ammunition

ŠPaul M. Alvarez 2003

"That's a great price on that ammo, but it's corrosive". We have all had the same trepidation when looking for shootable quantities of our favorite military ammunition. The price is right, but do we really want to deal with the problems inherent in shooting corrosive ammunition? Is it going to ruin my gun and leave me with a mass of rusted out steel? In actual point of  fact, corrosive ammunition is not very much harder to cope with than non-corrosive ammunition if you use a bit of common sense and some readily available materials.

We, as shooters, have been living with corrosive ammunition since the advent of gunpowder. As all blackpowder shooters know, you have to clean your gun as soon as possible after shooting or it will turn into a mass of useless rusty metal overnight. In humid climates it may only be a matter of hours. Then you get to do it again the next day. The residues of blackpowder fouls the bore and absorbs moisture like a sponge.

The advent of smokeless powder eased our burden somewhat but did not eliminate it. It used to be thought that the smokeless powder produced an acid during combustion and that this caused the barrel corrosion. Thus, various "nitro solvents" were developed, typically around a base of Amyl Acetate and various oils. This worked to some extent but required repeated cleanings over a period of several days to perform a thorough job. The cleaning mechanically removed some of the salts and the watery solution dissolved more of it. The oil would prevent the moisture from being absorbed for a time until it evaporated, then you were right back where you started with the remaining residue absorbing moisture over time.

The true cause of the corrosion was discovered by Dr. Wilbert J. Huff of the U.S. Bureau of Mines and reported by him in 1922. Most ammunition was loaded with chlorate primers, that is, they contain Potassium Chlorate as their main component. Upon firing this chemical breaks down into, among other things, Potassium Chloride. Potassium Chloride is a close relative of Sodium Chloride, aka common table salt, and is extremely hygroscopic, that is it absorbs and retains water from the humidity in the air. This in turn is what leads to the corrosion. The more humidity the more corrosion. However, his research also showed that below 50% humidity the corrosion did not develop even after several days until such time as in increased beyond that point. 

Up until the mid-part of the 20th century most all military ammunition was loaded with corrosive primers. Commercial ammo had been using non-corrosive primers for quite some time before that as RWS in Germany had developed a non-corrosive primer in 1901. Remington began their research and development of their "Kleanbore" priming based on the German patents and put it on the market in 1927. Virtually all U.S. commercial ammunition has been loaded with Lead Styphnate based non-corrosive primers since about 1930.

However, a major shortcoming of some these early primers was that they  had a short life span, sometimes of only a few years. Some early tests by Frankford Arsenal with non-corrosive primers also showed signs of excessive pressures. The military powers of the world needed a primer that was reliable and proven to hold up for extended periods of storage and so continued to use corrosive primers in their ammunition (with the notable exception of the Swiss, all U.S. .30 M1 Carbine, and some late-war Canadian ammo in .30-06).

The vast majority of the military ammo produced in WWII,  was corrosive primed. This was the case throughout most of the 1950s as well. The U.S. military switched to non-corrosive primers in the early '50s but many foreign militaries did not until much later.  Be suspicious of a seller claiming that his 1950's era ammo is non-corrosive. Some will tell you that it is "mildly corrosive", that is like being "mildly pregnant". When in doubt, and it always pays to be on the safe side, do a "nail" test and be sure.

To perform the nail test first take a piece of 2x4 lumber and drive a few common steel nails into it just far enough to hold them firmly in place. I like to buff them on a wire-wheel to make sure that I am down to the bare metal. Pull a bullet from a suspect cartridge, dump the powder, and load the empty case into your firearm. Now, with just the primed case in the chamber, point it at the board, making sure that it is in a safe direction, and fire it at the nails. Assume that the ammo is corrosive and thoroughly clean your firearm! Let the board with the nails stand for a few days and monitor for corrosion. If rust develops within a day or two then you are assured that it is corrosive. If not, then you either have non-corrosive primers or very low humidity. If the humidity is below 50% the rust may not show up for some time, if at all. Of course, any steel material may be used for the test. Some have advocated razor blades and steel wool. Any suitable material should work.

Corrosive ammunition will not harm your barrel if it is cleaned promptly and thoroughly. If you cannot clean the firearm immediately, the liberal use of WD-40 will usually protect it for a day or two. Over the years there have been many remedies for preventing the corrosion. The oldest and most common one is to use hot soapy water to dissolve the salts and residues in the barrel. This is the process that is commonly used by blackpowder shooters and works fairly well with the exception that it can cause rust itself. Most of us are rather adverse to running water through our prized rifles as well.

Ammonia solutions also seem to work quite well. Window cleaners containing ammonia such as Windex are convenient to use as well as other cleaners such as Parson's Ammonia. Soak a brass bristle brush in it and run it through the bore to loosen up any residue. Then soak a patch with the solution and run it through the bore to swab out the residue. Follow up with clean patches until the bore is clean and dry. For best results, repeat. Finish by using a polarized type of gun-oil such as Outer's 445. The polarized oils have an affinity for the the steel and soak into the crevasses to protect the bore. And don't forget to clean the bolt-face.

The best method is to use the old G.I. Rifle Bore Cleaner. It was developed specifically to clean the residues of the corrosive primers and works extremely well. It is used just as you would any other bore cleaner as outlined above. It's downside is that it is getting hard to come by as it is not produced any more and that it is carcinogenic as it contains Nitro-benzene. If you use this solution  make sure that it is in a well ventilated area and wear gloves and eye protection. Probably a good idea when using any bore cleaners. I have a box of surgical gloves purchased at a medical supply house for this very purpose. When done I just toss the whole mess in the trash. Common dish washing gloves also work well.

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My can, found at a local yard sale for $1, is marked "POISON" and SPEC. RIXS-205, REV. 1, P.O. No. (28-024) 44-40700.5 and was manufactured by S.C Johnson & Son, Inc. in Racine, Wisconsin. Directions for use read as follows:

"Run several cloth patches (each thoroughly saturated with fluid) back and forth through the bore until it is thoroughly scrubbed. Run two or three dry patches through the bore to pick up the dissolved salts. If the gun is to be used shortly, a fresh patch, wet with fluid, can be run through the bore and left wet. Otherwise, oil according to regulations."

So keep on shooting that cheap ammo and just remember to keep it clean.


Email: Omega Crossroads