7.62x39 Corrosive: The Fiery Soviet Surplus Survivor

 

7.62x39 Corrosive: The Fiery Soviet Surplus Survivor

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.

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.

Berden Primer and Boxer Primer: To grasp corrosive versus non-corrosive ammunition fully, it's essential to explore primer history briefly. The percussion cap preceded the contemporary primer, replacing the intricate flintlock ignition method, and when incorporated into the cartridge, it evolved into the primer we recognize today.

Primer Origins: Modern primers received patents in 1866 in England and the US as distinct designs: the Boxer and Berdan systems, named for their creators. New Yorker Hiram Berdan devised his approach—more prevalent in Europe—concurrently with Englishman Henry Boxer's design, which prevailed in North America.

Anvil Distinctions: The primary distinction lies in anvil placement, as primers require an anvil: the firing pin compresses the impact-sensitive compound against a firm surface for reliable ignition. Boxer primers integrate the anvil within the primer itself, whereas Berdan primers feature it in the cartridge case. External inspection won't reveal the primer type, but removing the bullet and powder exposes it—a central flash hole above the primer pocket signals Boxer priming, while off-center flash holes (typically one to three) across the pocket denote Berdan.

Regional Usage In North America: Boxer priming dominates sporting and commercial ammo production, yet Berdan-primed rounds persist in military surplus from Europe, Russia, and Asia. North American shooters often meet corrosive ammo in these imports, fostering a myth that equates Berdan with corrosiveness and Boxer with non-corrosiveness—but primer type bears no relation to corrosiveness; it's determined by the primer compound.

Primer Chemistry Shift: Primer chemical evolution proves complex, suiting only deep scientific study, so a simple overview suffices: North American commercial primers shifted to non-corrosive formulations around 1931, barring rare cases. US military ammo lagged until the 1950s due to rigorous government standards unmet by initial non-corrosive mixes, which faltered in long-term storage reliability—critical for war reserves. Other nations adopted the change later or not at all.

Left Berden Primer, Right Boxer Primer

A scope Cam's view inside the casing of 7.62 x 39 ammunition

Chemical Components of the Corrosive Primer: All primers, regardless of chemical composition, are composed of three major compounds; there’s always an explosive to get things started, an oxidizer to provide oxygen for the burn, and a fuel for the reaction. These will make up about 90% of what’s in the primer, with an additional 10% of miscellaneous materials. The most common composition currently in use is comprised of 40% lead-styphnate acting as the explosive, 40% barium-nitrate as the oxidizer, 10% antimony-sulphide as fuel, and 10% miscellaneous materials. These primers are considered non-corrosive, but note the presence of heavy metals, especially lead. That lead in the primer contributes significantly to the airborne lead generated by a gunshot, and since lead is a hazardous material, manufacturers are working hard to get rid of it, and thus create the next generation of primers. The issue with corrosive primers lies in the oxidizer, which is potassium chlorate (KClO₃). When the primer is ignited, the reaction removes the oxygen atom from this molecule, leaving potassium chloride (KCl). Unfortunately, potassium chloride is a salt, much like sodium chloride, our commonly used table salt. And as a salt it’s hygroscopic, meaning it attracts water. Mix water with salt on top of a steel surface, and rust, with its associated pitting, is guaranteed. That’s our problem.

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. You’ll note that sodium chloride is table salt. 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).

Corrosiveness Link: Corrosiveness stems from potassium chlorate in the primer compound, not the primer type both Berdan and Boxer can be corrosive. However, corrosive primers are commonly paired with Berdan in surplus ammo because post-WWII Eastern Bloc manufacturers standardized Berdan for steel cases and corrosive formulations.

Key Differences Between Berdan and Boxer Primers:

The most fundamental difference between these primer systems lies in anvil location. Berdan primers utilize an anvil formed as part of the cartridge case, while Boxer primers contain the anvil within the primer itself. This distinction creates several important functional differences between the systems. Flash hole configuration represents another key difference. Berdan-primed cases feature multiple flash holes positioned around the central anvil, while Boxer-primed cases utilize a single central flash hole. This difference significantly impacts the reloading process, as Berdan cases require specialized tools to remove spent primers. Production costs also differ between the systems. Berdan-primed ammunition typically costs less to manufacture because the primers lack internal anvils and the cartridge cases require no machining for a central flash hole. Boxer primers cost slightly more to produce due to the more complex primer assembly containing the internal anvil.

Advantages of Berdan Primers:

Berdan primers offer several advantages that explain their continued use in global ammunition production. Manufacturing efficiency stands as a primary benefit. Berdan-primed cases typically cost less to produce than their Boxer counterparts because the primers contain fewer components and the multiple flash holes can be easier to form during the case manufacturing process. Reliability represents another advantage of the Berdan system. The multiple flash holes ensure ignition even if one hole becomes partially obstructed. This redundancy can provide more consistent ignition under adverse conditions. Additionally, the integral anvil in the case tends to withstand multiple firings with less deformation than the separate anvils in Boxer primers. Water resistance provides another benefit of Berdan-primed ammunition. The multiple small flash holes create less direct exposure between the primer and the main powder charge, potentially offering better protection against moisture intrusion. Some military ammunition continues to use Berdan primers for this reason, particularly in regions with challenging environmental conditions.

Cost Russian manufacturers almost exclusively load berdan primers in steel cases. Steel is a significantly cheaper metal than brass, which is why Berdan-primed ammo is nearly always more economical than Boxer-primed alternatives.

Affordability Berdan primers cost less to manufacture than Boxer primers. The difference is slight and might not be obvious. Berdan-primed ammo is usually significantly cheaper because it is also steel-cased. Regardless, you do wind up paying less for primers when you opt for Berdan-primed ammo over Boxer-primed alternatives.

Safety Berdan primers are slightly less sensitive to slamfiring than Boxer primers. They are seated just beneath the surface of the case instead of flush with it, so a free-floating firing pin has a lower chance of accidentally igniting a Berdan primer when the firearm is dropped or otherwise violently jostled.

Disadvantages of Berden Primers:

Performance and Reliability Steel cases are cheaper than brass ones, but they pose two major disadvantages in terms of performance. First, steel is more rigid than brass, so steel cases are less effective at sealing the chamber during ignition. This means more propellant residue can enter the action, which in turn leads to accelerated fouling of the firearm. Second, shooters often have more failures to feed and extract with steel cases over brass. In general, steel cased ammo performs less reliably than brass cased ammo.

Reloadability Rigid steel cases do not return to their original dimensions following ignition. Reloaders must manually resize them before reloading them, which is time-consuming. Furthermore, a Berdan-primed steel case’s anvil gets worn down when it is struck by the firing pin, which is fiendishly difficult damage to undo.

The Berdan primer itself poses two major hurtles to handloaders. First, Berdan primer sizes are not nearly as standardized as Boxer primers. Getting the correct size of Berdan primer for a given round of ammunition can be difficult (especially since component Berdan primers themselves are rare). Second, correctly lining up a Berdan primer with its two flash holes is tricky – and a step you don’t have to worry about at all while you’re reloading Boxer-primed ammunition.

Corrosiveness Modern Berdan-primed ammo is uniformly non-corrosive. Shooters often assume that Berdan-primed ammo is corrosive because they are accustomed to old Soviet era military surplus, which is indeed loaded with obsolete corrosive primers that will cause rust without special cleaning after firing. Old Boxer-primed military surplus ammo may be corrosive as well, but corrosion simply isn’t something you have to worry about when the ammo has been recently produced for the commercial market.

Advantages of Boxer Primers:

Boxer primers offer significant advantages that have made them the standard in American ammunition manufacturing and the preferred choice for reloaders worldwide. Reloading compatibility represents the primary benefit. The single central flash hole allows spent primers to be pushed out from inside the case using a simple pin or rod, making primer removal straightforward with basic reloading equipment. Primer availability constitutes another advantage. Boxer primers are produced in greater quantities and varieties in the United States, making them readily accessible to both ammunition manufacturers and reloaders. Common sizes include small pistol, large pistol, small rifle, and large rifle primers, each available in standard and magnum versions. Consistency also favors Boxer primers. The self-contained anvil design ensures uniform ignition characteristics across production batches. Additionally, the single flash hole provides a more direct ignition path to the powder charge, potentially offering more uniform powder ignition.

Reliability Boxer-primer  ammunition commonly features brass cases. Brass cases are more supple than steel cases, which in turn promotes more reliable feeding and extraction. Their superior suppleness also permits brass cases to return to their original dimensions following ignition, in which state they are easily reloadable.

Reloadability  Boxer-primed ammo is the easiest to reload. There are two main reasons for this aside from the suppleness of brass. First, Boxer primer sizes are heavily standardized. Most rounds of Boxer-primed ammunition require either a small pistol, large pistol, small rifle or large rifle primer. (There are some exceptions, like the 50 BMG which requires its own dedicated primer.) Second, because the Boxer primer’s single flash hole is centrally located at the base of the shell casing, it requires no effort to correctly line up the two components while handloading.

Disadvantages of Boxer primers

Cost Brass is the best metal for shell casings, but the alloy is about 60% copper. Copper is known as a “semi-precious” metal for good reason: It is relatively expensive, so brass-cased ammo tends to cost significantly more than steel-cased or aluminum-cased alternatives.

Manufacturing Defects Boxer primers occasionally leave their manufacturers with defects that compromise their performance, such as a misplaced anvil. Such manufacturing defects are exceedingly rare, however, and they are not exclusive to Boxer primes by any measure. In fact, Boxer-primed ammo is nearly always more reliable than Berdan-primed alternatives.

Which Ammunition Uses Berdan Primers?

Berdan primers appear most commonly in ammunition manufactured outside the United States, particularly from Eastern European, Russian, and Asian producers. Military surplus ammunition from these regions almost exclusively utilizes Berdan primers. Common calibers found with Berdan primers include 7.62x39, 7.62x54r, 5.45x39, and various European pistol calibers. Several commercial ammunition manufacturers continue to use Berdan primers in their production, particularly for ammunition lines where reloading considerations hold less importance. Berdan primers appear most frequently in steel-cased ammunition marketed as economical practice or range ammunition. Additionally, some hunting ammunition from European manufacturers continues to utilize Berdan primers. Notably, many corrosive ammunition offerings, both commercial and military surplus in nature, utilize Berdan primers. Berdan primers which are corrosive are corrosive due to the presence of potassium chlorate. Upon ignition, the potassium chlorate in a corrosive primer disperses corrosive salts into the bore and action of the firearm. This is not to say that all Berdan primers are corrosive by any means. In fact, there are many noncorrosive Berdan-primed loadings on the market.