#Bullet

Today we’ll be looking at a round with one of the strangest-looking projectiles ever designed for a military weapon: The joint Heckler & Koch-CETME 4.6x36mm round designed for the HK36 en-bloc clip fed assault rifle. The rifle was, as the name suggests, developed by HK, and based on their successful family of roller-retarded blowback rifles, including the G3, MP5, and HK33. It fed from an unusual fixed 30-round magazine, which was loaded from the side through a panel with a polymer 30 round en bloc clip. The projectile was developed by Gunther Voss, of CETME, the very same who invented the unique aluminum-cored projectiles for the 7.92×40 CETME a couple of decades earlier.

Information on this round and the weapons designed to fire it is scarce, so the details in this article may be at times incorrect. Just letting you know. -NF

In a previous post about the sometimes ambiguous meaning of the word “caliber”, we discussed how the word had mutated through the centuries, picking up different definitions and connotations along the way. In that article, I wrote:

How can one balance the trade-offs inherent in ammunition design to create a true one-caliber infantry weapon system that is both effective and lightweight? This is a question I’ve been exploring for close to a decade, and writing about for over four years. The question is extremely compelling to me because so much is demanded of the answer: Unlike with two-caliber systems, all the needs of the infantry must be met with one single caliber configuration, so each and every dimension must be carefully measured to allow the lowest possible weight, which is arguably the most important single characteristic of small arms ammunition.

We’ve discussed a lot of different rounds in this series so far, but today we’re going to discuss a round that actually has a shot of being adopted (at least in some form) by the United States military as a next-generation small arms ammunition configuration. That round is the .264 USA, developed over the past few years by the Army Marksmanship Unit (AMU).

Previously, we discussed the benefits of and challenges facing saboted projectile ammunition, including the advantages of decoupling the diameters of the bore and the projectile, and the problems of accuracy during sabot discarding. One concept that could possibly provide many of the benefits of saboted projectile ammunition without the drawbacks is the idea of having a malleable projectile that is forced through a conical section of bore, squeezing it down to a smaller shape. This increases, to a degree, the swept volume of the barrel, while not requiring any discarding sabot and not producing “wasted” energy that goes into propelling the mass of the sabot out of the barrel.

After World War II, US Army analysts determined that the effectiveness of the infantryman was not as closely related to their marksmanship discipline as had been previously thought. It seemed that instead, the random environmental circumstances and effects, plus the concealment and movement of the target, had much more of an influence on the probability of a hit than the ability of the shooter to fire his weapon with precision. With this knowledge in hand, arms designers in the West set out to improve the chances of the soldier to hit his target, and the most obvious solution was to simply send more lead downrange. The simplest way to do that was, of course, to create ammunition that fired more than one projectile per round.

One of the problems of small arms ammunition is that of swept volume. That is, the most ballistically efficient projectiles are the longest and thinnest ones, which cut through the air more easily than squatter, fatter projectiles. Yet, the best projectiles from a propulsion perspective are the widest ones, as they have the most area at their base for the expanding gases to push on, making them more efficient, especially from shorter barrels.

It’s not just the Yanks that are getting improved ammunition: Our friends across the pond have developed their own firepower upgrade for 5.56mm and 7.62mm weapons alike. Jane’s has a modest article on the subject, while The Register provides a quite good overview of exactly what the new rounds are and what they mean for today’s Tommy:

After World War II, the nations of the world retired to lick their wounds and rebuild, but their arms engineers also began thinking about the next war. The war have brought forth a storm of new technologies and inventions, and one of the most significant in the field of small arms was the finally mature assault rifle in the form of the Nazi-developed “Sturmgewehr”, and its intermediate 7.92x33mm Kurzpatrone cartridge. One nation that took notice of this new weapon and its ammunition was the newly reconstituted Czechoslovakia. That nations engineers quickly took to copying and improving the 7.92 Kurz caliber, producing by the early 1950s a short-lived but unique round called the 7.62x45mm Kr.52, or more popularly the 7.62×45 Czech. The 7.62×45’s projectile was a near copy of the Kurzpatrone’s stubby, steel-cored one, but its case was much longer, while being slightly thinner, and having a greater internal volume. This gave the Czech round an additional 250 ft/s muzzle velocity versus the German 7.92×33 when fired from the barrel of the rifle that was designed alongside it, the strange but wonderful vz. 52.

What happens when you take the two concepts of a traditional, full-power rifle and machine gun round, and a small-caliber, high-velocity round, and smash them together? You get one of the most extreme military small arms calibers ever developed, and one of the last small arms projects from the twilight of the Soviet Union.

In the mid-1950s, the People’s Republic of China followed the Soviet Union’s example and adopted the intermediate 7.62x39mm round. This decision substantially helped to promote that cartridge’s ubiquity throughout the world, as millions of cheap Chinese-made SKS and AK rifles were exported to every corner of the globe. However, at the very end of Chairman Mao Zedong’s regime, an effort was started to develop a new, modernized caliber that would improve performance and conserve materials versus the 7.62×39. That program resulted in the 5.8x42mm caliber, standardized in the late 1980s with the DBP-87 and DBP-88 rounds. Unusually, the 5.8x42mm used a system with two different overall length standards, one of about 58mm for the DBP-87 rifle cartridge, and the other of about 62mm for the DBP-88 support round. This allowed the marksman’s rifle to shoot the DBP-87, if necessary, but also allowed for a longer, lower drag bullet to be put in the DBP-88 case, improving the ballistics of the QBU-88 marksman’s rifle and the QJY-88 general purpose machine gun.

Shouldn’t “Modern Full Power Calibers” be its own series? No, because then there would only be two episodes! So instead, we’re rolling today’s two most popular full power .30 cal rounds into the series on intermediates, primarily as comparison pieces. There are really two pieces of information I want to disseminate with this, which are the answers to “how do these full power rounds compare with intermediate calibers?” and “how do they compare against each other?”

On Saturday we looked at one British  “contender” which could have in some alternate reality become the NATO standard round, and today we’re going to look at another: The 4.85x49mm. After the United States adopted the .223 Remington round as the 5.56x45mm in the mid-1960s, a race began among NATO member nations to create and adopt something similar. Lest the Organization lose the benefits of standardization if a member nation pre-emptively adopted a new SCHV round, these efforts force NATO to begin a competition for a second NATO-standard infantry round. Entrants from the USA, France, Belgium, Germany, and the UK competed head-to-head, and while it was the Belgian 5.56mm SS109 that emerged victorious, the 4.85x49mm round submitted by the UK was ballistically impressive enough to warrant a second look.

Among the interesting concepts that were tested in the mid-late 20th Century is that of an extremely light for caliber, very long bullet made in part of a lightweight material like aluminum and plastic. The 7.92×40 CETME, which if I can find a specimen I will cover later on, is one example, but starting in 1972 the now-closed Frankford Arsenal began experiments on 5.56mm cases loaded with super-long projectiles with von Karman ogives, with the aim of creating a lightweight round using a low-density projectile and an aluminum case. Original testing was conducted with full-length 5.56mm cases and two lengths of bullets, but eventually a shortened brass case and a 37gr bullet with the same shape as the shorter initial test bullet was created. As a solution to the problem of burn-though with aluminum cases, the Arsenal developed a plastic insert called a “flexible internal element” (FIE), and the brass cased rounds developed for ballistic testing also had FIEs. This shorter round in both aluminum and brass cased forms was called the 5.56x38mm FABRL, which stood for “Frankford Arsenal – Ballistics Research Laboratory”, and this at some point was made into a backronym for “Future Ammunition for Burst Rifle Launch”.