Many of us shoot military surplus ammunition with corrosive primers in our SKSs (M43, you're shooting collectable ammo?!, or M67), Mosins, Mausers, etc. I all too often see misinformation on various boards, and especially on Facebook, and I figure every board should have an informative discussion of the subject, so here we go. I apologize ahead of time for perhaps getting too deep into the chemistry, but I'm a biochemist and I actually enjoy this stuff
Sodium chlorate, NaClO3, or potassium chlorate, KClO3, based primers
The chlorate anion, ClO
3-, is the main active ingredient and serves as a the percussion sensitive oxidizer in this type of primer. Chlorate is only slightly more reduced (by one pair of electrons) than the even stronger oxidizer sodium perchlorate NaClO
4, used in solid rocket fuel formulations. Chlorate is the source of chloride, Cl
-, in the spent residue from the primers, i.e., the sodium chloride (table salt) or potassium chloride, which are the active “corrosive” ingredients. Humans need sodium, potassium and chloride, so these residues are harmless from a human health perspective. (I find it a bit ironic, that we are more concerned with our rifles than our own health in respect to the inhalation of lead aerosols from the discharge of modern non-corrosive lead styphnate based primers, but that's another subject).
The use of the terms corrosive ammo or corrosively-primed ammo (more specific) is a bit of a misnomer and often leads to confusion. In the chemical hygiene sector, the term
corrosive usually refers to something acidic, like battery acid (sulfuric acid), or muriatic acid (hydrochloric acid) and hence in need of neutralization. This is not true in the case of simple salts like sodium chloride and potassium chloride. They are pH neutral (neither acidic nor basic), their corrosiveness is based largely on their ability to attract water from the air and trap that water adjacent to the steel surfaces of the bore (these salts are hygroscopic). Water is needed to mediate the oxidation of metallic iron to ferric oxide (rust) by oxygen in the air, so trapping water and maintaining it in contact with the iron of the bore is the problem posed by the corrosive primers. To prevent corrosion, these salts need to be removed from the bore. This cleaning should take place as soon as possible if high relative humidity (over 50%) conditions are in effect at the time of firing your rifle, or during storage thereafter. If one lives in an arid climate, then cleaning is less urgent, but should still be done soon, because relative humidity varies with the weather and time of day (it is temperature dependent), even in arid climates.
Inorganic salts like sodium chloride and potassium chloride are very soluble in water and slightly soluble in ethanol or methanol. Water and alcohol are examples of polar solvents, and that is the general type of solvent needed to solubilize any type of salt (salt is used in the general sense here, not specifically referring to table salt). Non-polar solvents like petroleum distillates found in aerosol or liquid gun oil formulations, paint thinner, mineral spirits, etc. are not effective at dissolving salts.
The cheapest way of dissolving and removing salts is the use of water. Of course you don’t want to leave any water behind when you’re done cleaning, because attraction of water is the problem with salts in the first place! Using hot water can aid in evaporation, as long as there is enough volume of hot water to heat up the barrel, and thus speed drying. Following up with a wet denatured alcohol (ethanol) patch or two is another method since water and ethanol are completely miscible and the ethanol is more volatile, i.e., evaporates more quickly. If you prefer a commercial cleaner, then choose something like Hoppe’s No. 9 Solvent, which has a lot of ethanol, and run a series of soaked and dry patches through your bore. Such a procedure is probably sufficient to dissolve and wipe out the relatively low amount of salts produced by corrosive primers. If you’re a black powder shooter, Hoppe’s No. 9 Black Powder Cleaner is an even better alternative to their regular Solvent formulation, since it’s about 80% water. Just follow it up with dry patches and a water displacing solvent like standard Hoppe’s #9 Solvent. It’s not my intent to endorse Hoppe’s products as the ultimate solvents, they’re just widely available examples of suitable products. I like to finish my bore cleaning with an oiled patch. Then I run a dry patch through the bore before heading to the range. Of course your preferences may vary.
Aside: Windex almost always comes up in "corrosive ammo" discussions, and this cleaner is okay as the primary salt removing solvent, since it’s mostly water. However, it needs to be followed up with a water displacing solvent, as discussed for the water or black powder cleaner methods mentioned above. The Ammonia D
TM (actually just dilute ammonium hydroxide) is a mild base. At higher concentrations ammonium hydroxide is uniquely effective at removing copper fouling--but again, that’s another chemistry subject. I don’t think there’s sufficient ammonium hydroxide in Windex to be particularly useful in removing copper. If copper removal is your aim, then you can use Sweet's Bore Cleaning Solvent, or simply dilute some household ammonia 1:4 with water.