Some Further Arguments About The GPC/6.Xmm Infantry Rifle Ammunition

I've done a little arguing here and there on forums about the general purpose cartridge (GPC) idea, and the closely related but not necessarily identical 6.Xmm rifle cartridge concept, and I feel it is worth reposting some of the posts I've made for reference here on the blog.

First, here's a discussion of how shorter barrels negatively impact the GPC concept, relative to 7.62 NATO. One might think that if a GPC equals 7.62 NATO in capability from a 24" barrel, that the same round should equal 7.62 NATO if both are shot from 16.5" barrels, right? This is not in fact the case. What can be seen here is that 7.62 NATO retains its energy at range more gracefully as barrel lengths get shorter than a 6.5mm round.

The way the model is set up, 7.62 NATO data was pulled directly from empirical figures, and in either case - 24 or 16.5" barrel - the 6.5mm's velocity was adjusted to match the energy at a kilometer.

Perhaps this is somewhat of an opaque example, and I should later go into greater depth exploring it, but for now, I am just reposting it here:

Alright, here you go guys, here's a demonstration of how shorter barrels hurts the GPC more than 7.62 NATO. Let's use Rifleshooter's test of Winchester contract overrun as a baseline. So, from a 24" barrel, that ammunition produces a muzzle velocity of 2909 ft/s. Here's what it looks like at a klick:

445.9 J, that's what we have to match with the GPC. I am using a 6.5mm near-Balle D homologue for this, i7 FF of .889 and a G7 BC of .249, 108gr/7g. I adjusted the velocity until it matched 7.62 at a klick from a 24" barrel:

That the MV ended up identical to .264 USA is coincidence. Note that the projectile used is much, much finer. So the round has to produce 2,875 ft/s from a 24" barrel to match 7.62 using that exceptionally fine bullet. Now, from a 16.5" barrel, the Winchester produces 2,682 ft/s:

410.3 J. So we have to match that with our 6.5mm:

So there you have it. Internal ballistics aside, even the best 6.5mm GPC loses out to 7.62 NATO as barrels get shorter. Note that 7.62 NATO retained 92% of its muzzle velocity when the barrel was shortened by 7.5", but to catch up to that, the GPC has to cling to over 97% of its muzzle velocity.

Next is a post I wrote addressing the idea that 7.62x54R "overmatches" 7.62 NATO to any substantial degree. This is a commonly held view, but it appears to be the product of some suspect ballistic coefficient figures posted to 7.62x54r.net:

The most common light steel cored ball ammo has a BC very similar to M80, and generally speaking a slightly lower or equal muzzle velocity.
I would be very surprised to hear that the more exotic types - especially the 7N1 - were at all common in Afghanistan, and I also have doubts about their "legendarily" high BCs.
For example, let's take the 7N1 "sniper" ball, pulled bullet alongside propellant and case below:

Clearly not a bad bullet shape, but how good is it? The ".249 G7 BC" figure was translated from G1 BC from 7.62x54r.net's website, the same site where I took this image. In fact, the round in this image was pulled from the very same sample of rounds tested. So there is no question that the data matches the projectile. But does the data make sense? In short, no. A .249 G7 BC means this 152gr projectile has a .907 i7 FF. What other projectiles have about a .907 i7 FF? Well:

The best, most streamlined examples of the 7.9mm sS Patrone had an i7 FF of about .906. And,

The new Berger 130 AR Hybrid ogive bullet, with its i7 FF of .919.
Both of these bullets are considerably better streamlined than the 7N1. Coming at it the other way, let's look at the plain-jane steel-cored light ball projectile, which according to 7.62x54r.net has a BC (converted) of .163 G7, which would give it a hilariously poor i7 FF of 1.34:


Note that the ogive is identical to the tangent ogive of the 7N1, and that the boattail is not too much less severe.
Because of this, I cannot consider 7.62x54r.net's BC figure for the 7N1 to be likely. It's much, much more likely that the i7 FF of these projectiles is in the 1.10-.98 range, giving the 7N1 a BC of .229 G7, at best. Given the lower velocity, this makes it ballistically extremely similar to 7.62x51.
If you look at Hodgdon's numbers for 7.62x54R and mate those with 7.62x54r.net's BC figure for the 7N1, the round looks quite scary, but the velocities produced by actual military ammunition, coupled with more realistic estimates of the BCs of military projectiles give much more sedate ballistics.

The only way that the Russian caliber could be overmatching 7.62 NATO substantially would be if Russian AP ammunition were finding its way into the hands of enemy combatants. Not only is there little evidence that this is happening, it means the correct response would be to field a round with more penetration than current M80 Ball - which is exactly what the US Army has done with the M80A1.

Another post addresses the danger of over-emphasizing the need for fine projectile shapes. Certainly, projectiles should have as fine a shape as feasible, however often a fine shape is not compatible with other requirements, such as the shape of an armor penetrating core:

That doesn't really make sense. The shorter ogive was chosen because the ogive they were using - retained from the earlier .30-06 M2 - was short enough that the bullet could be buried more deeply in the case. Later, the form factor was improved by going to a 10-caliber secant ogive.
The 7.62x51 NATO was further specifically designed for a 700m danger space requirement, falsifying what you said about it being designed for shorter ranges. Even if I've misunderstood you and you were referring to 5.56mm, that round was designed for a 500m requirement.
You cite the 7.9x57 sS Patrone, but that round is the exception, rather than the rule.  The 7.9x57 was not designed with an ogive that long; the earlier S Patrone being almost identical in shape to the aforementioned M2 Ball. The fine ogive of the sS ball was applied later, and they mostly got away with it because the 8mm projectile was so wide. The AP core for the SmK round is in fact smaller in diameter than that of the .30 caliber M2 AP, despite the projectile being .381mm wider. It could not be any wider, or else it wouldn't fit into the fine form factor - the same form factor as the sS Patrone.
So you can see that having a fine ogive has consequences, which is why even in rounds like the 6.5x55 Swedish Skp. Ptr. 41 the ogive is not that long, surprisingly. This all goes back to what I've been saying for some time now; while it's nice to have a fine ogive shape, at the end of the day having the finest projectile shape with the lowest i7 FF puts limitations on your projectile design, and less elegant projectiles not bound by those limitations may actually perform better.

It's also worth noting that the shape of the projectile of one kind of round influences the shape of others. A poorly shaped tracer projectile may not match the trajectory of the ball round closely enough, and an AP round that required a different zero than the ball ammunition would be much less useful than one that didn't. At the end of the day, all these requirements must be met, and these can drive poorer projectile shapes than the GPC crowd often assumes.

This next post is an explanation of why it is difficult or impossible to compensate for a lack of MG teams by augmenting the capabilities of the rifleman's weapon:

I think it's worthwhile, too, to take a tangent and discuss why rifles firing more powerful ammunition cannot compensate for a lack of machine gun teams. I'll make it short, I hope.
The machine gun team consists of  the gunner and assistant gunner, which - like a sniper and his spotter - gives it much better situational awareness than a single rifleman. Both the gunner and assistant gunner are well-trained to make the most of this relationship, and are equipped to provide fire at longer ranges, and are given a tripod and tracer rounds to assist them in this. When you hear things like "800m is crew served weapons range" this is what is meant. Two men with the right equipment can provide accurate fire out to much longer distances than is possible with one person with a rifle, in combat conditions.
For example, let's examine what happens when the trigger is pulled against a target at longer ranges (over 200 yards). The hammer falls, and the cartridge ignites. Immediately, the gun begins to recoil under great acceleration, and flash and blast emanates from the weapon's muzzle, obscuring vision for just a moment. Within that moment the round has traveled a considerable distance downrange, and the further out it impacts, the less visible the impact is, both because the impact is more distant and because there is less velocity to the impact. The round will most likely not hit the target, due to a wide variety of errors that are impossible to consistently compensate for on the first round. If this is a rifleman, he is likely to blink during firing, and the recoil of the gun disturbs his sight picture - his rifle is after all not equipped with a tripod, and his ammunition is not (usually) traced, so he has a harder time distinguishing the trajectory of his fire. Now, if this is a machine gun team, the AG is sitting there watching all this happen. He has seen where the round has gone, as much as is possible, and the gun is properly equipped with a tripod and tracers, not to mention a T&E mechanism. Being a machine gun, too, fire comes in bursts, improving the probability of a hit. The AG is dedicated to assisting the gunner in putting out accurate fire - he has no other job (besides keeping the gun fed). His eyes help the gunner pick out targets, and he's able to tell the gunner immediate feedback that the gunner otherwise would not have - like when a civilian is sighting a rifle in on the range, having a spotter is a huge help; at longer ranges it's essential.
So for this reason, I strongly contest the idea that a lack of MG teams can be compensated for by issuing more powerful rifles. No, a lack of MG teams can only be compensated for by fielding more MG teams.

The subjects of these posts will probably be combined at some point in a larger more in-depth article for The Firearm Blog, but with the Light Rifle and daily posts currently occupying my time, I cannot say when that post will arrive.

An Evaluation of The Faxon Firearms ARAK-21 Rifle

At the event Faxon Firearms hosted on January 22nd of this year, I had the chance to shoot some examples of the Faxon ARAK-21 rifles, especially two rifles, which I will call Fifty-Two in 5.56mm and Oh Five in .308 Winchester (the latter of which I am given to understand is a prototype). I shot other ARAK-21s, but what I will say here concerns these two in particular.

Fifty-Two, with EoTech, suppressor, ACE folding stock, and short handguard.

With Fifty-Two, I had numerous malfunctions, mostly of a minor kind that was nonetheless indicative of more serious problems the rifle may have. The weapon had a tan finish, was suppressed, with a short handguard, ACE folding stock, and it mounted an EoTech holographic sight. I assume the barrel was in the 13-16" range; I do not know exactly how long. I chose to shoot this weapon because it was in 5.56mm, had a short handguard (so I could make a more fair weight comparison to other rifles), and because I wanted to get as much trigger time on one rifle as possible. I was not led to shoot this particular rifle by any Faxon employee or anyone else. I estimate I put less than a hundred rounds through Fifty-Two. It was the rifle I shot the most at the event.

Fifty-Two had already been shot before I reached it; I am not sure when it was last cleaned, but thanks to the suppressor the rifle already had a fine film of powder residue inside the receiver. I did not consider this residue further in my analysis.

Fifty-Two's receiver was very dirty, but no dirtier than I would expect from a suppressed AR-15 after firing a few hundred rounds.

I first made some ergonomic observations about the rifle, before shooting it. Even with the ACE folder, which I hoped would add some weight to the rifle and improve its balance, it was very front heavy; I found this created significant discomfort when handling the weapon, especially when compared to an M4-style carbine. Other rifles of the current generation are also front-heavy, but I would consider Fifty-Two to be exceptional in this regard.

I noted the rifle's charging handle sits forward and very low over the rail, and folds. I found the charging handle difficult to grab in this position; essentially I could only hold onto the very tip. Before I began shooting, I noted the bolt had to be given a running start to go into battery. When charging the rifle, this became a serious problem. If Fifty-Two has a bolt-closure device, I did not discover it (I was later informed that the ARAK-21 does not have a bolt-closure device). For comparison, even AR-15s without forward assist devices can be assisted into battery by pushing against the carrier with the thumb; there is no ability to do this with Fifty-Two. While I would normally consider pushing the bolt into battery a minor problem, I found that Fifty-Two presented serious problems when trying to correct this malfunction. The bolt head was able to capture cartridges and strip them from the magazine through friction alone, causing combined bolt-over-base/double-feed malfunctions when trying to close the bolt. I had to either remove the magazine and try to feed a new round, or carefully short-stroke the gun to achieve battery; this happened several times.

Fifty-Two, and all other rifles I have fired, had serious heating issues. Even firing magazines of only 5 rounds each, which was how ammunition was provided at the event, the rifles retained heat and quickly became uncomfortable to hold with bare hands. This happened much sooner than I would have expected in a similar string of fire with my Colt 6920 (which uses old-style Magpul MOE handguards). The pace of fire was very tame. I would go to the line, shoot one or two magazines with five rounds a piece, return to the ammunition station, pick up one or two more magazines of five rounds, and repeat. I did not try to do this as fast as I could. Despite this, the rifle heated up substantially. It also held the heat long after I set it down to cool.

The recoil of Fifty Two, and all other 5.56mm ARAK-21s I shot on the 22nd, was not so mild as reviews of this firearm led me to believe. I did not shoot an AR-15 at the event, but it's my opinion that the ARAK-21 recoils somewhat harder than my 6920. The ARAK-21 most likely has softer recoil than standard AKM-type rifles, in my opinion. Given the weight of the rifle, I would consider its recoil characteristics acceptable but marginal.

The malfunctions I experienced with Fifty-Two were mostly failures to engage the bolt hold open device. The rifle would tend to overshoot the bolt catch and be stopped by the follower of the magazine. These malfunctions are indicative of a very high cyclic rate and high friction during feeding, which is consistent with the observations I made on how fast the bolt seemed to be cycling. I did not bring my high speed camera, and thus could not confirm the cyclic rate.

I field-stripped Fifty Two without the aid of a Faxon representative. However, I did feel there were improvements that could be made to the field-stripping process. Depending on how it is counted, field stripping requires four or five steps to complete, while assembly requires five steps. During assembly, I found the enclosed receiver hindered alignment of the piston with the gas tube, and that it was possible to get the bolt carrier inside the receiver without having the piston properly aligned in the tube. The delicacy needed to get the piston and bolt carrier aligned in their respective homes caused me more than once to compress the bolt during assembly inadvertently. Unlike an AR-15, it is possible to insert the bolt assembly into the receiver with the bolt in the rearward locked position, which prevents correct assembly. After I had disassembled the gun the first time, I still found the process of field strip and reassembly to be a balancing act. It is my opinion that both the AK and AR-15 are much easier to strip and reassemble than Fifty-Two, especially under duress. Fifty-Two was the only ARAK-21 I field stripped.

Fifty-Two had a gas regulator. After firing a modest number of rounds, I found the gas system too hot and too small to manipulate. Given the rifle's high cyclic rate, I feel this is a significant drawback. The rifle when I got it had the cyclic rate turned all the way to the right, if one is looking down the sights. I do not know whether that position is all the way on or at the minimum setting.

I also fired rifle Oh Five in .308 Winchester. This rifle suffered similar failures to go into battery as Fifty-Two. I shot far fewer rounds through Oh Five, perhaps ten or fifteen. My shooting with Oh Five was ended when the Fiocchi ammunition that was provided blew a primer out of the back of the case, sticking in the chamber and causing a double feed. Examination of brass fired through Oh Five showed signs of pressure: The imprint of the dual ejectors was visible on the case head, having been etched through the headstamp. This is not the first time I have seen signs of dangerous pressure from Fiocchi ammunition. It is my opinion that these malfunctions were not the result of any flaw in the rifle, but rather the ammunition manufacturer's fault. At this point, I called a representative over and he retired the rifle for the day.

Oh Five, with a blown-out primer. I have no reason to believe this was the fault of the rifle.

I have provided pictures of a little less than half of the malfunctions I encountered in shooting less than 100 rounds, embedded below. Each picture documents a separate malfunction. I have also included some pictures of Fifty-Two's condition during firing, showing how it was configured and the dirt inside of the receiver.

A typical malfunction in Fifty-Two was for the bolt to skip over the cartridge base and try to feed it into the chamber through friction from the bolt lugs. Skipping over the cartridge base is a sign of either worn out magazines, which is unlikely, or a rifle that is running far too fast.

The follower of the PMags provided produced enough friction against the bolt to stop the moving parts group. I believe this rifle cycled all the way to the rear, but skipped over the bolt hold open, another sign of a rifle that is running at too high a cyclic rate.

Fifty-Two had considerable difficulty in locking and achieving battery. The bolt as seen here has stopped against the barrel, and failed to rotate. This malfunction is caused by a poor mass ratio, ejectors with too powerful springs, and friction in the receiver. In Fifty-Two, this malfunction was needlessly difficult to overcome, due to a lack of options for manually closing the bolt. Even AR-15s without forward assists can be manually assisted into battery by pushing with the thumb against the bolt carrier. Fifty-Two has a slick-sided bolt carrier that prevents such a maneuver.

If I attempted to fix the bolt closure problem, this malfunction would often result. The first cartridge has remained in the chamber, never captured by the bolt's extractor, while the bolt has picked up the second cartridge through friction alone, causing a combination of bolt-over-base and double-feed malfunctions.

In my opinion, rifle Fifty-Two had some serious limitations. I am not sure exactly what segment of the market Faxon is targeting with the ARAK-21, but based on my shooting experiences on the 22nd of January with rifle Fifty-Two, I would not be able to recommend the ARAK-21 at this time. The rifle has serious issues stemming from a moving parts group that is too light and a mass ratio that is too poor. Faxon has tried to fix this by increasing the cyclic rate, but this most likely caused failures to eject and round skipping. It's probable that the Faxon engineers added the stronger ejectors and a gas regulator to solve those problems, but these in turn cause problems of their own. The Faxon ARAK-21 needs a total redesign to properly solve these issues.

The Taylor Knock-Out Index Is Useless

This article was originally posted on another blog of mine in early 2012, but its content is more appropriate here, I think.

The Taylor Knock-Out Index may be the single worst metric available for determining the effectiveness of small arms ammunition. Despite this, it sees relatively widespread use, usually to compare two calibers that are obviously in different potency classes.

Why does the TKOI suck so bad?

Well, let's do an experiment: What is the Taylor Knock Out Factor of the Lambert Glacier?

Of course, if you stand in front of the glacier, you'll hardly get vaporized. Glaciers, unless you're on poorly navigated, fast-moving ships, are largely harmless.

And yet...

The TKOF equation goes something like this:

TKOF = (Mass x Velocity x Caliber)/7000

Units in the normal Imperial grains, feet/sec, and inches, of course.

So what's the TKO of the Lambert Glacier?

Well, the Lambert Glacier is about 100km wide, 400km long, and 2.5km deep.

To get volume, simply multiply:

100,000 x 400,000 x 2,500

= 100,000,000,000,000, or 100 trillion cubic meters volume.

The density of ice is 916,700 g/m^3

The mass of the Lambert Glacier is estimated to be approximately:

91,670,000,000,000,000,000, or 91.67 sextillion grams mass.

To find mass in grains, we simply multiply that by 15.43:

91.67 x 15.43 x 1 sextillion

=1,414,468,100,000,000,000,000, or 1.41 septillion grains mass.

What is the caliber of the Lambert Glacier? We'll go ahead and take its width and height, and average them:

(100,000m + 2,500m)/2

= 51,250m

Multiply by 3.28 and 12 to convert to inches:

=2,017,200, or 2.02 million inches.

What is the velocity of the Lambert Glacier?

It varies, but one source quotes 400 to 800m/year Let's do some quick math:

(400 + 800)/2

= 600 m/yr

600 m/yr x (1/(60x60x24x365)) yr/s

= .000019 m/s

.000019 m/s x 3.28 ft/m

= .0000624, or 62.4 microfeet per second

Now we can plug it all in!

TKOF = (Mass x Velocity x Caliber)/7000

TKOF = (1,414,468,100,000,000,000,000 x .0000624 x 2,017,200)/7000

Before we solve this equation, we need some reference. For comparison, a 7.62x51mm rifle round has a TKOF of 17.787, and a .45 ACP pistol round has a TKOF of 12.568.

Now, the Taylor Knock Out Factor of the Lambert Glacier is...

Wait for it...

Wait for it...



25,434,829,886,052,571,429 TKOF! That's over twenty five sextillion on the TKOI! The Lambert Glacier should have destroyed the Earth by now!

Quake in fear at the might of the Lambert Glacier, Destroyer of Worlds!

All My TFB Posts On The M1 Garand

The M1 Garand has been the subject of much of my writing over at TFB, since it is a fascinating design, at once revolutionary and deeply flawed. Its descendant, the M14, is to this day a controversial weapon; at once the longest serving rifle and the shortest serving standard issue rifle in U.S. military history, it's a rifle that will virtually always deeply polarize a conversation with its mention.

I have decided to collect the posts I have so far done on the M1 Garand and the M14 rifle, for the convenience of my readership. They are, in chronological posting order, as follows:

Hindsight Is 30/06: A Critique Of The M1 Garand
Making The M1 Garand
The Great Rifle Controversy: 1955
Eight Reasons Selfloading Rifles Had To Wait For John Garand
Rifle Competition: US vs. UK in 1950 (DTIC)
InRange TV’s Heinous M1A Abuse
Small Caliber Book Reviews: U.S. Rifle M14, From John Garand To The M21
Two USMC Marksmanship Training Films Compared
The M1 Garand In The Dust And Mud, 1950

I will definitely be posting more about these rifles in the future; in particular, I have upcoming a post on the "light rifle" concept, as full-power automatic infantry rifles were once called, which I hope will prove to be a definitive design case study on that concept.