#Bullet

In this installment, we’ll be looking at a very unique round. The 6mm SAW was probably the first small arms round ever designed using computer-calculated parametric analysis, and it was also probably the first American rifle round designed from the outset for steel cartridge cases. The initial design parameters were for a round effective to 1,000 meters, and which accepted a tracer that would give a visible daylight burn out to 800 meters, and this resulted in a caliber of 6mm with a 105 grain slender steel-jacketed lead-cored bullet possessing a high length/drag ratio. Although fired at modest velocity, the sleek bullet retained its energy extremely well, giving the round good long-range penetrating power, especially compared to the 5.56mm rounds at the time. Ultimately, the 6mm SAW succeeded in its ballistic goals, but was rejected on logistical grounds, as the idea of fielding three different rounds (5.56mm, 6mm, and 7.62mm) was not considered feasible.

The 6x35mm TSWG, also commonly called the 6x35mm KAC, is a round shrouded in mystery. Apparently designed by Knight’s Armament Company for the interagency counterterrorist program cryptically named the “Technical Support Working Group” alongside the PDW with which it is popularly associated, the round was apparently never adopted. However, it is interesting primarily as an example of a round with shorter overall length than the standard 2.2-2.3″ (56-58mm) OAL that has become ubiquitous for modern intermediate rounds. The 6x35mm TSWG was designed solely for the unique KAC PDW, but a more traditional AR-15 type rifle called the SR-635 was also chambered for it. Like the .300 Blackout, the 6x35mm was also designed explicitly for 10″ or shorter barrel lengths; KAC has advertised their PDW as being available with 8″ or 10″ barrels. To properly compare the round with both the .300 Blackout and 5.56mm, we will be looking at estimated velocity figures from both 9″ and 14.5″ barrels, although it should be noted that so far as I know, no weapons chambered for the 6x35mm cartridge actually exist with barrels of either of these lengths:

In the late 1950s, after the first public demonstrations of the AR-15 and its new small caliber, high velocity cartridge, the Soviet Union took notice of the radical developments in military .22 caliber rounds in the United States. By 1959, four years before the adoption of the AR-15 as the M16 by the US Army, Soviet ballisticians were already testing Soviet-made replica 55gr spitzer FMJ bullets fired at over 3,000 ft/s from modified necked down 7.62x39mm cases. This program for a new small caliber high velocity lasted into the late 1960s, but it wasn’t until the mid-1970s that the 5.45x39mm caliber was eventually issued alongside the AK-74 rifle, a modified but significantly more effective variant of the previous 7.62x39mm AKM assault rifle.

Like the .300 AAC Blackout that we discussed earlier, the 7.62×40 Wilson Tactical was intended to be a medium-performance .30 caliber cartridge that would function in standard AR-15 type rifles with minimal modifications, such as a barrel change. Also like the .300 AAC Blackout, the Wilson round was based on an earlier wildcat, which was designed by Ken Buchert and also called the 7.62×40. Unlike the .300 Blackout, however, the 7.62x40mm Wilson Tactical sacrificed some versatility for raw power in the form of a lengthened case based on the 5.56mm case, instead of the .221 Remington Fireball used by the Whisper/Blackout. This longer case gives the 7.62×40 WT a significant performance advantage over the .300 Blackout from comparable barrel lengths, but it limits how ballistically efficient the projectiles used by the round can be. In theory, the 7.62×40 WT can also be loaded with subsonics, like the .300 AAC Blackout, although the short ogive length limits which COTS bullets can be used for this, and no factory subsonic ammunition exists for the Wilson round. This makes the 7.62×40 WT virtually a dedicated supersonic hunting or 3-Gun round (in which it makes Major Power Factor), but it is still worth considering in our discussion. Now, on to the ballistics:

What if there was a caliber that was suitable for everything from coyote to brown bear, kicked less than your whitetail gun, fit in a micro-length (2.25″/58mm) action, and cost a quarter a round to shoot? That would be a pretty awesome caliber, wouldn’t it? It turns out that this caliber might already exist, if the industry can fulfill its potential: It is the Russian 7.62x39mm caliber used by the infamous AK-47 rifle.

Previously, we looked at the incredible damage and penetration caused by the US Army’s new M855A1 Enhanced Performance Round (EPR), thanks to a video published by William of the Wound Channel. What happens, though, when that kind of performance is scaled up to .30 cal size and fired from a .308 Winchester? William has us covered there, too:

In the second installment of Ballistics 101, we took a look at the concept of a “ballistic coefficient”, or a drag model based on an empirically tested projectile, against which other projectiles can be measured and compared. Mentioned in that post – but not explained – was the concept of form factor, which is the subject of today’s installment.

A trend towards ever more powerful and longer-ranged ammunition was cut short by the realities of the First World War: Technologies not previously invented or accounted for, such as the man-reaping machine gun and the portable infantry mortar, made the existing infantry tactics of long-range volley fire not just obsolete, but quaint. Further, new essential small arms projectile designs like tracers, armor piercing bullets, and exploding observation rounds demanded more space in the projectile envelope, putting the previously cutting-edge small-caliber 6.5mm rounds at a disadvantage. The advantages of these small-caliber rounds were virtually negated, too, by the advent in 1905 of the German S-Patrone, a flat-based, pointed projectile that was vastly more efficient in supersonic flight than previous round-nosed designs. Although French engineers preceded this design with the superior (and top secret) Balle D round, it was the German bullet that became the pattern for military rifle projectiles worldwide.

On my recent article “Ballistics 101: What Is Ballistic Coefficient?”, commenter Anthony asked for clarification on some points:

Thanks to John C. for sending us this our way via Facebook.

“Caliber”. It can mean a lot of different things, but when we use it, what does it really mean, and what’s its significance?

I don’t consider myself more than a hobbyist when it comes to ammunition – I reload a little, play around in SolidWorks a bit, and read dry, dusty tomes full of other people’s hard work collating every minute detail about ammunition. I’m, frankly, an ammo nerd, but not really a true expert. Once I began writing, however, I found that very few people are ammunition nerds, at least in the same way that I am.

A TFB reader recently 3D Printed 9mm caliber bullets and loaded them 9mm Luger/Parabellum cases with subsonic and supersonic loads. The bullets were printed with PLA, a bio-plastic made from corn starch in the USA or sugar cane elsewhere in the world. PLA is commonly used in 3D printers as an alternative to ABS plastic (think lego bricks). It is easier to print (at least in my experience) than ABS requiring lower temperatures and it has a pleasant non-toxic smell.

Tony Faulkner posted his creation in a local firearm group on Facebook. It is an exploded representation of a bullet’s components. This one is made from a Winchester 30-06.

I am not sure what to call this type of malfunction. Yesterday, I went to the range with a co-worker. He brought along his Browning Hi-Power. On the last round, of a shooting string, this happened. He said he felt a pop and then mushy trigger. He looked at the chamber and saw the malfunction, which you can see in the picture above.