Wednesday, November 20, 2013

Steel-Cored Armor Piercing Loads for 5.56mm

As body armor improves and as the presence of lightly armored vehicles increases on the battlefield, it is reasonable to expect that inexpensive steel cored armor piercing rounds will become more desirable. Currently, there are 5 steel cored armor piercing loads widely available, in all calibers: .30-06 M2, 7.62x51 M61, 7.62x54R BP, 5.45x39 7N22, and 5.8x42 DBP-10.

These loads provide a good starting point for designing a new steel-cored AP round for the 5.56mm.To gain some idea of the effectiveness of each projectile's core, we will examine their respective length-to-diameter ratios, gleaned from images of the sectioned bullets. Unfortunately, I was unable to find any reference material for the Russian 7.62mm BP projectile. The rest are as follows:

M2: Between 4.1 and 4.6 calibers, depending on sample 
M61: Between 3.3 and 3.7 calibers, depending on sample 
7N22: 5.2 calibers
DBP-10: 4.9 calibers

Because the M2 and M61 cores have such uncompetitive L/D ratios, we will forgo scaling those projectiles down, and instead focus on analogues to the 7N22 and DBP-10.

Scaling the 7N22 projectile to .224" caliber, we get a weight of 59.9 grs and a length of 1.020". Doing the same for the DBP-10, we get a weight of 60.7 grs and a length of 1.015. So far, both bullets seem very comparable, with the 7N22 projectile having a somewhat higher ballistic coefficient.

Bullet seating will be calculated both for the intended depth of the original 7N22 ammunition, and to fit within 5.56mm's OAL, respectively. The former produces a figure of 2.488" overall length.

The 5.8mm caliber has two versions: one intended for rifles, and one intended for DMRs and machine guns. The former has an overall length of 58mm, while the latter has an overall length of 61mm. The case length is 42mm, giving the each bullet 16mm and 19mm of exposure, respectively. We will use these figures, adjusted for caliber to 15.19mm (.598") and 18.03mm (.710"), as well as the original figure for 5.56mm of 12.70mm (.500") to give us overall lengths for each.

Utilizing the Powley Computer, we can determine performance for all five configurations:

Fig. 1: 5.56mm with scaled down 7N22 bullet and the same relative seating depth as 5.45mm

Fig. 2: 5.56mm with scaled down 7N22 bullet

Fig. 3: 5.56mm with scaled down DBP-10 bullet and the same relative seating depth as 5.8mm heavy ball

Fig. 4: 5.56mm with scaled down DBP-10 bullet and the same relative seating depth as 5.8mm light ball

Fig. 5: 5.56mm with scaled down DBP-10 bullet

Fig. 6: A hypothetical 60gr steel-cored 5.56mm AP load
As we can see, performance is very similar for all types. The ideal configuration might be found in an adapted DBP-10 projectile - perhaps with a proportionally larger core - designed to fit within the existing 2.26" OAL of 5.56mm. This would give comparable performance to the DBP-10 within 500m, and cause minimal logistical disruption. The projectile could have reverse-drawn jacket with closed tip giving it a good ballistic coefficient and excellent accuracy, while conforming to international treaties. The finished product might look something like the render in figure 6.

Sunday, November 10, 2013

The Case Against a General-Purpose Cartridge

Despite my efforts to keep to one system, this article hops between metric and imperial units quite a bit. Often, alternate units will be contained within parenthesis following a figure, but it's always a good idea to keep conversion factors handy when working with small arms. I use 25.4 millimeters to the inch, 3.28 feet per meter, 145 PSI per MPA, and 15.43 grains per gram.

Anthony Williams - an internet military enthusiast, collector, and author - is the primary online proponent of the universal rifle/machine gun caliber. The General-Purpose Cartridge, as he calls it, would theoretically combine the lethality and range of a 7.62mm weapon with weapons and ammunition closer to 5.56mm systems in weight. While he never lays out the requirements for such a round in an organized fashion, a clear picture can be formed from select lines in his article:

This indicates that the muzzle energy, weight and calculated recoil of the GPC should be approximately midway between the 5.56 and 7.62 - similar to the 6.8 Remington and 6.5 Grendel.
The bullet's performance at 1,000 metres should be comparable with the 7.62 M80 ball, as measured by hit probability (a function of trajectory, flight time and susceptibility to wind drift) and damage potential (bullet energy and penetration).

Is the GPC as envisioned by Mr. Williams and his fellows possible? Is it desirable? Is it cost-effective? Previously, I have been very taken the idea of a unified rifle and machine gun cartridge for the military. As a result, I am highly familiar with the multitude of variations on this same concept: ranging from .276 Pedersen copycats, to kurz cartridge revivals, to miniaturized big game hunting magnums, to Mr. Williams' ambitious 6.5/8/800. While the focus of this article is primarily to address the GPC, I will argue that, relative to the 5.56mm and 7.62mm cartridges now in service, all of these proposals fail to satisfy at least one of the three criteria. Some are technically feasible and perform better than either 7.62 or 5.56, but not enough better to warrant the expense and logistical disruption needed to field them. Some are technically feasible, but offer no advantage over the existing calibers while being saddled with significant downsides. Finally, some, such as Mr. Williams' 6.5/8/800, are simply technically unfeasible as currently imagined.

The first group of cartridges all greatly resemble (though none improve upon) the .276 Pedersen. These include the 7x46mm UIAC, the .270 Sidewinder, the .280 British, and others. The second-most mature group, many have examples have actually been loaded and fired, and the .280 British was even officially adopted, briefly. Because their performance has been verified, it cannot be said that these cartridges are unfeasible, but is it worth the cost and effort to field one, in light of the widespread adoption of 7.62mm weapons? In a word, no. Even the literature for 7x46mm UIAC shows it's not greatly more efficient than 7.62 NATO, and it doesn't provide any additional capability, so why would military procurement spend millions re-arming with entirely new weapons and ammunition when they have almost-as-good-and-already-in-the-inventory 7.62 NATO machine guns and rifles? Since these cartridges are also almost as heavy as 7.62, they offer little practical benefit and will be largely passed over.

Due to a growing sense of doubt about the effectiveness of 5.56, numerous cartridges that I would characterize as belonging to the second category have been proposed. These include the 6.8 SPC, the .300 Blackout, the 7.62x40 Wilson Tactical, and more obscure cartridges, like the 6mm-223, 6.5x42 MPC, 6.8mm ARC, and 6x41mm SCC. These cartridges all share greater projectile mass and lower velocity than 5.56mm, and relatively small cases, so that existing 5.56mm rifles can be rechambered for them, if necessary.

My analysis of this category will be short: They are a technological step backwards. Their low velocity (typically not above 800 m/s, with some even below 700 m/s) and non-exceptional projectiles (typically with low sectional densities comparable to 5.56mm) produce ballistics inferior to that of the M4 Carbine in terms of trajectory, while offering little to no more energy at range for every pound carried. Most of the literature on these cartridges stresses their superior energy at range per shot to 5.56mm. Usually, this is true, but these cartridges come saddled with so much extra weight compared to 5.56mm that the advantage, if there was any there in the first place, is moot. A short example is as follows:

Input Data
Ballistic Coefficient:0.151 G7Caliber:0.224 in
Bullet Weight:62.0 gr
Muzzle Velocity:2950.0 ft/sDistance to Chronograph:10.0 ft
Sight Height:1.50 inSight Offset:0.00 in
Zero Height:0.00 inZero Offset:0.00 in
Windage:0.000 MOAElevation:0.000 MOA
Line Of Sight Angle:0.0 degCant Angle:0.0 deg
Wind Speed:10.0 mphWind Angle:90.0 deg
Target Speed:10.0 mphTarget Angle:90.0 deg
Target Height:12.0 in
Temperature:59.0 °FPressure:29.92 in Hg
Humidity:0 %Altitude:0.0 ft
Vital Zone Radius:5.0 in
Std. Atmosphere at Altitude:NoPressure is Corrected:Yes
Zero at Max. Point Blank Range:NoTarget Relative Drops:Yes
Mark Sound Barrier Crossing:NoInclude Extra Rows:No
Column 1 Units:1.00 inColumn 2 Units:1.00 MOA
Round Output to Whole Numbers:No
Output Data
Elevation:6.951 MOAWindage:0.000 MOA
Atmospheric Density:0.07647 lb/ft³Speed of Sound:1116.4 ft/s
Maximum PBR:305 mMaximum PBR Zero:261 m
Range of Maximum Height:147 mEnergy at Maximum PBR:740.6 J
Sectional Density:0.177 lb/in²
Calculated Table
10/11/13 18:34, JBM/jbmtraj-5.1.cgi

Input Data
Ballistic Coefficient:0.180 G7Caliber:0.277 in
Bullet Weight:110.0 gr
Muzzle Velocity:2550.0 ft/sDistance to Chronograph:10.0 ft
Sight Height:1.50 inSight Offset:0.00 in
Zero Height:0.00 inZero Offset:0.00 in
Windage:0.000 MOAElevation:0.000 MOA
Line Of Sight Angle:0.0 degCant Angle:0.0 deg
Wind Speed:10.0 mphWind Angle:90.0 deg
Target Speed:10.0 mphTarget Angle:90.0 deg
Target Height:12.0 in
Temperature:59.0 °FPressure:29.92 in Hg
Humidity:0 %Altitude:0.0 ft
Vital Zone Radius:5.0 in
Std. Atmosphere at Altitude:NoPressure is Corrected:Yes
Zero at Max. Point Blank Range:NoTarget Relative Drops:Yes
Mark Sound Barrier Crossing:NoInclude Extra Rows:No
Column 1 Units:1.00 inColumn 2 Units:1.00 MOA
Round Output to Whole Numbers:No
Output Data
Elevation:8.926 MOAWindage:0.000 MOA
Atmospheric Density:0.07647 lb/ft³Speed of Sound:1116.4 ft/s
Maximum PBR:275 mMaximum PBR Zero:234 m
Range of Maximum Height:130 mEnergy at Maximum PBR:1155.8 J
Sectional Density:0.205 lb/in²
Calculated Table
10/11/13 18:24, JBM/jbmtraj-5.1.cgi

We can see the top chart refers to 5.56mm M855 from a 16" barrel, and the bottom to 6.8 SPC from the same length barrel firing 110 gr Hornady BTHP bullets. Higher velocities have been achieved by 6.8 SPC from this barrel length, but not - to my knowledge - with factory ammunition.

6.8 SPC does offer 56% more energy at half a kilometer than 5.56mm (not three or four times as much energy, as I've heard it claimed more than once), but what is that per kilogram? M855 weighs about 12 grams and provides about 34 kilojoules of energy at 500m per kilogram of ammunition carried. 6.8 SPC weighs about 17 grams with a 110 grain bullet, and provides about 37 kilojoules of energy at 500m per kilogram, ten percent more than M855. Is a 25% worse trajectory, increased bolt stress, lower reliability, fewer rounds per magazine, and the introduction of an entirely new cartridge worth a 10% increase in energy per kilogram at half a kilometer? Keep in mind that, due to its large case, good sectional density, and fairly high velocity, the 6.8 SPC is one of the best performers in this category of ammunition.

The third category contains cartridges that either have never been made or are not what they are advertised to be. Examples include the 6mm Optimum, Mr. Williams' 6.5/8/800, and the 6.5 Grendel. Only one of these actually exists - the 6.5 Grendel. To many, the existence of the Grendel proves the GPC concept's viability, but a closer examination shows that is not the case. There are numerous problems with the 6.5 Grendel, first and foremost being its unsuitability for military applications. Beyond (valid) concerns about the cartridge's extreme shoulder angle and lack of case taper, the case itself does not have enough internal volume to accept tracer or steel-cored armor piercing projectiles, except with the lightest bullets. Thus, it cannot fulfill the role of a GPC, as it is not a suitable military cartridge. Further, the 6.5 Grendel provides low levels of performance with factory loads, only achieving its much-touted velocity and trajectory with delicately loaded handloads using very slow-burning and often compressed powders. For field purposes, it is a 7.62x39 with better bullet selection.

Enter the 6.5/8/800, the hypothetical "ideal" general-purpose cartridge proposed by Mr. Williams in his opus. Is this cartridge feasible, and if so, does it offer enough of an advantage to ISAF/NATO members to warrant its adoption and the retirement of both the 7.62 and 5.56 calibers? Mr. Williams' has only provided us with with visual mockups of his cartridges via his website, so the only way to find out is to design the cartridge for him. As per his requirements, the cartridge will be 6.5mm caliber, have an 8 gram bullet, and produce a muzzle velocity of 800 meters per second from a 20" barrel.

Using a combination of CAD modelling and this online Powley Computer, I created a virtual cartridge that met these specifications, so that we can see if it might be a suitable replacement for 5.56mm and 7.62mm.

The first hurdle to jump was the design of the bullet. Mr. Williams specifies that the bullet should be based on the 7N6 projectile of the Russian 5.45x39 cartridge, which would meet both the good form-factor and lead free requirements. However, simply scaling that projectile up yields a bullet weight of only 5.9 grams (less if it is constructed without any lead at all, as the 7N6 incorporates a lead sleeve and plug), far short of the 8 gram requirement. In the end, I designed my own lead-cored bullet, based on the 7N6, to meet the weight requirement, which came to an overall length of 33.5 millimeters, or 1.32 inches for the imperial-unit Powley Computer. One could also use the existing 123 grain Lapua Scenar and get much the same results, since that projectile is 1.295 inches (32.9mm) long. One final note on projectiles: Because of its heavy, high form factor bullets, the GPC already devotes much of its internal and external volume to accommodating the projectile, which, even lead-cored, is already 13% longer than M80 ball's projectile. The lead-free armor-piercing and tracer projectiles necessitated by the cartridge's military application will only aggravate this problem, and may result in the cartridge's weight spiraling significantly to maintain performance. While Mr. Williams does acknowledge this problem, he does not make any attempt to address it.
Fig. 1: The case of the 6.5x50mm GPC, with dimensions

Next, I had to design the case (Fig 1). This was to be a challenge, as utilizing the .30 Remington case (also used by the 6.8 SPC, and favored by Mr. Williams) proved unfeasible due to excessive length needed to attain the requisite performance while maintaining adequate case taper and shoulder angle (.8 and 20 degrees, respectively). I turned instead to the 7.62x45mm Czech for the case head, and attained a case length of 50mm before the performance goals were met. The cartridge now fit within the requisite 2.8" (71.1mm) overall length of 7.62 NATO, and with 45 grains water (2.92 mL) case capacity, was capable of propelling its projectile to 800 m/s within 57,000 PSI (390 MPa) peak pressure, from a 20" barrel (Fig 2).

Fig. 2: The data entered into the Powley Computer

Fig. 3: The completed GPC

With the case and projectile finished, and the specified performance achieved, all that was left was to weigh the cartridge and calculate its recoil. The volume of the brass case was 1.109 cm^3, resulting in a weight of 9.43 g. The weight of the powder charge was 2.35 g (36.3 grains), and the bullet, of course, was 8 grams. To calculate the weight of a large rifle primer, I set five together on my powder scale, weighed them, and averaged the result, which was approximately .35 g. When summed, the 6.5x50/8/00 weighed 20.13 grams; more than two grams heavier than Mr. Williams' initial estimate, and nearly 70% heavier than 5.56mm.

To fully evaluate the cartridge, it was necessary to calculate its recoil energy. The correct formula for this is as follows:

mB = mass of bullet in kilograms  
mP = mass of powder in kilograms 
vB = velocity of bullet at muzzle in m/s 
vP = velocity of powder gas at muzzle m/s  
mF = mass of the firearm in kilograms  
mC = impulse of the cartridge, in kilogram-meters per second 
eF = energy of the firearm, in joules 

The impulse of a cartridge can be expressed as:
mC = mB * vB + mP * vP 

and its energy when fired from a firearm of a certain weight as:
eF = [(-mC)^2]/2mF

The velocity of the propellant gases of modern small arms rifle cartridges is described as being about 4,000 ft/s (1,220 m/s) in this paper from the end of WWII. Using this value, 4kg for the weight of the rifle, the values calculated for the 6.5x50/8/800 above, and 1.69 and 2.92 grams for the charge weights of the M855 and M80 ball, respectively, we can calculate the recoil energy of the GPC, 5.56, and 7.62, for comparison:

5.56x45 M855: 5.9 kg-m/s impulse, 4.3 J energy
7.62x51 M80: 11.5 kg-m/s impulse, 16.7 J energy
6.5x50/8/800: 9.3 kg-m/s impulse, 10.7 J energy

With two and a half times the recoil energy of 5.56, and over one and a half times as much impulse, it's doubtful that it could be an effective replacement for that cartridge in all but the heaviest small arms. While this level of recoil is not too far outside Mr. Williams' initial estimates, I contend that they do not allow the cartridge to be chambered in the light, small, carbines that are now popular, especially in echelon roles. Therefore, the GPC cannot effectively replace 5.56mm.

While this all may sound very negative, there is a silver lining: the cartridge produced about a 20% superior trajectory to 7.62 at 1,000m, along with providing about 15% additional energy at that range with significantly reduced recoil energy. Indeed, while overweight, and having excessive recoil, the cartridge seems superior to 7.62mm in most respects.

Since we have designed a cartridge that meets our performance requirements, and we have some idea of how much it weighs, how would replacing 5.56 and 7.62 with it affect the burden of the infantry platoon? Using the figures from this report on infantry combat loads, we can get some idea.

The infantry platoon in the US Army contains three infantry squads, a weapons squad, and a platoon headquarters.

In each of the three infantry squads, there is the Squad Leader armed with an M4 Carbine, two Team Leaders armed with M4 Carbines, two Automatic Riflemen armed with M249 SAWs, two Grenadiers armed with M4 Carbines and attached M203 GLs, and two Riflemen armed with M4 Carbines.

Weight of ammunition (only, not including magazines or links) of infantry squad breakdown by squad role: 
Squad Leader: 210 rounds 5.56mm, totaling 2.54 kg
Team Leader: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totalling 4.96 kg (x2)
Automatic Rifleman: 800 rounds linked 5.56mm, totaling 9.68 kg (x2)
Grenadier: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totaling 4.96 kg (x2)
Rifleman: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totaling 4.96 kg (x2) 
Weight of ammunition of infantry squad: 51.7 kg (x3) 
Weight of ammunition of infantry squad with 20 gram GPC: 85.4 kg (x3) 
Weight of ammunition of infantry squad with M240s in place of M249s: 85.5 kg (x3)

In the weapons squad, you have the Squad Leader armed with an M4 Carbine, two Machine Gunners armed with M240 GPMGs, two Assistant Gunners armed with M4 Carbines, and two Ammunition Bearers armed with M4 Carbines.

Weight of ammunition (only, not including magazines or links) of weapons squad breakdown by squad role: 
Squad Leader: 210 rounds 5.56mm, totaling 2.54kg
Machine Gunner: 300 rounds linked 7.62mm, totaling 7.26 kg (x2)
Assistant Gunners: 210 rounds 5.56mm in magazines, 400 rounds linked 7.62mm for M240 totaling 12.22 kg (x2)
Ammunition Bearer: 210 rounds 5.56mm in magazines, 300 rounds linked 7.62mm for M240, 140 rounds 7.62mm in magazines totaling 13.2 kg (x2) 
Weight of ammunition of weapons squad: 64.5 kg 
Weight of ammunition of weapons squad with 20 gram GPC: 63.8 kg

In the platoon headquarters, you have the Platoon Leader armed with an M4 Carbine, the Platoon Sergeant armed with an M4 Carbine, the Radio Operator armed with an M4 Carbine, the Combat Medic armed with an M4 Carbine, and the Field Artillery Forward Observer, also armed with an M4 Carbine.

Weight of ammunition (only, not including magazines or links) of platoon headquarters breakdown by squad role 
Platoon Leader: 210 rounds 5.56mm, totaling 2.54 kg
Platoon Sergeant: 210 rounds 5.56mm, totaling 2.54 kg
Radio Operator: 210 rounds 5.56mm, totaling 2.54 kg
Combat Medic: 210 rounds 5.56mm, totaling 2.54 kg 
Weight of ammunition of platoon headquarters: 10.2 kg 
Weight of ammunition of platoon headquarters with 20 gram GPC: 16.8 kg 
Total weight of ammunition in the platoon: 229.3 kg   
Total weight of ammunition in the platoon with 20 gram GPC: 336.8 kg 
Total weight of ammunition in the platoon with M240s in place of M249s: 330.9 kg 
Weight increase in the platoon if Carl Gustafs are issued in place of 60mm mortars: 47.5 kg

It is clear that replacing both 5.56 and 7.62 with a cartridge meeting the specifications of Mr. Williams' GPC, as much as that is possible, increases the weight of ammunition of the platoon well above the threshold of other more cost-effective solutions. In addition, 30 out of 38 personnel in the platoon are armed with M4 Carbines. If a GPC were adopted to replace 5.56, those rifles and magazines would have to be supplanted with larger weapons and ancillaries compatible with the new cartridge, adding further weight to the platoon. If being out-ranged is a major concern, issuing more 7.62mm caliber M240 machine guns in place of 5.56mm caliber M249s is a much more cost-effective solution than a complete conversion to a GPC cartridge, while having a similar increase in the weight carried by the platoon. If the problem lies with an inability to use mortars due to restrictive rules of engagement, it would be lighter to issue Carl Gustaf recoilless rifles as direct-fire assets in their stead, than to issue rifles and machine guns chambered for a GPC.

In conclusion, the GPC concept is one that is attractive only on paper. When rigor is applied, the cost of such re-armament in dollars, hours, and pounds is not justified by the new cartridge's performance. Mr. Williams' proposed cartridges utilizing the .30 Remington and 6.5 Grendel cases are unfeasible as they are conceived, and a cartridge resulting from his performance requirements is too heavy and has too much recoil to replace 5.56mm for most applications. The expectation that he could design a cartridge that produced the same performance as the 6.5mm Arisaka but with much lower weight and sized proved unreasonable. These sorts of errors are understandable, as Mr. Williams does not, to my knowledge, have experience loading ammunition.

A final note: Mr. Williams' intentions are good, but his concept seems to rely on an overly optimistic estimation of what infantrymen are capable of in terms of marksmanship at range. He thus perceives infantrymen armed with more powerful, longer-ranged rifles as having greater capability than those armed with 5.56mm carbines, when in fact, for the vast majority, the heavier cartridge and necessarily heavier rifles and magazines merely increase their burden. In short, giving long-range rifles to line infantrymen without additional training is a waste of strategic resources, money, and time. This is not to say that specialized marksmen would not be able to take advantage of such a cartridge, but they would be better served by a specialized rifle firing a cartridge with higher velocity and better hit probability at range, not the inherently compromising GPC.

Wednesday, October 23, 2013

Small Caliber, High Velocity Isn't New

There are some old fudder dudders who firmly believe that 5.56x45, .223, and similar and related calibers are a "fad" or a "failed experiment", especially for military use. Usually, they advocate a return to the full-power .308/7.62mm caliber as the end-all caliber, but some advocate for weaker calibers, like 6.8 SPC or 7.62x39. To all those who object, caliber is an important design consideration.

This post will be short: 5.56 and other small-caliber, high-velocity (SCHV) cartridges are not a fad. In fact, guns have been getting smaller and smaller in caliber, and higher and higher in velocity, for hundreds of years. Let's take a look at how infantry small arms have progressed in the 800 years or so that they've been around. (The historical overview section of this article is only intended as a cursory overview of the weapons in question. Details may have been omitted, glossed over, or compressed. I highly recommend seeking out further literature on these topics.)

1994 M4 Rifle, 62 gr .224" cal spitzer boat tail at approx 3,000 ft/s
1967 M16A1 Rifle, 55 gr .224" cal spitzer boat tail at approx 3,270 ft/s
1958 M14 Rifle, 147 gr .308" cal spitzer boat tail at approx 2,750 ft/s
1903 (1906) Springfield, 172 gr .308" cal spitzer boat tail at approx 2,640 ft/s
1903 Springfield, 220 gr .308" cal round nose at approx 2,300 ft/s
1892 Krag-Jørgensen Springfield, 220 gr .308" cal round nose at approx 2,000 ft/s
1873 Springfield Rifle-Musket, 405 gr .45" cal lead round nose at approx 1,350 ft/s
1868 Springfield Rifle-Musket, 450 gr .50" cal lead round nose at approx 1,250 ft/s
1853 Enfield Rifle-Musket, 530 gr .577" cal Minié ball at approx 900 ft/s
1700s "Kentucky" Long Rifle, ~140 gr .45" cal round ball at approx 1,500-2,000 ft/s
1717 Charleville Musket, 494 gr .69" cal round ball at approx 900 ft/s
16th Century Arquebus, 464 gr ~.68" cal round ball at approx 1,500 ft/s
14th Century Hand Gonne, 430 gr .66" cal round ball at approx 1100 ft/s

From the 18th century onward, we see a trend of ever-increasing muzzle velocity and decreasing caliber. The introduction of paper cartridges containing Minié balls allowed the use of rifle-muskets as standard infantry small arms, as they combined the ease of loading of a musket with the accuracy and range of a rifle. The introduction of the Minié ball also saw a reduction in caliber: from .69" to .58", with a slight increase in projectile weight. This resulted in much greater sectional density, which contributed to the greatly improved ballistic performance of the new rifle-muskets. Additional tests after the American Civil War showed that .50" and later .45" calibers offered even more improved performance. Eventually, .45" caliber metallic cartridges in the form of the .45-70-405 Government would be the standard for the United States for nearly two decades.

What would replace the breech-loading Springfield rifle-musket would be a smokeless powder foreign bolt action rifle firing a bullet nearly half the weight at nearly half again the muzzle velocity, the 1892 Krag-Jørgensen. The Krag would prove to have a very short service life, being replaced by the superior (and also foreign) Mauser design in the form of the 1903 Springfield rifle, possessing extremely high performance and a muzzle velocity of 2,300 ft/s. With the implementation of aerodynamic spitzer projectiles in the 1906 rifle, velocity again improved to over 2,600 ft/s, and bullet weight was significantly reduced. The example cartridge used is the M1 Ball load, introduced in 1926, but higher velocity loads like M1906 Ball and M2 Ball were used extensively, both of which fired ~150 gr flat based bullets at 2,800 ft/s. Since the .30-06 cartridge comes in almost endless variations with different bullet weights and velocities, the M1 Ball type used here is intended to be representative of the caliber in general.

The self-loading era begins with the M1 Garand, also in .30-06, producing performance very similar to that of the Springfield or M14, with a 150 gr flat-based projectile fired at 2,800 feet per second. Because for the purposes of this discussion, it is highly similar to the M14, it has been omitted. After WWII, a program was initiated to develop a lighter magazine-fed select-fire rifle, and resulted, after over a decade of research and testing, in the M14, which was only an incremental improvement over the Garand upon which it is based. The M14, like the Krag before it, would see service as a standard rifle for less than a decade, though it would continue to be used in specialist roles up to the present day.

The next significant innovation in small arms was what is sometimes called "small-caliber, high-velocity" ammunition, but which in reality was just a continuation of a trend stretching back hundreds of years. US Army studies again suggested that a smaller caliber, lighter bullet, fired at a higher muzzle velocity was desirable, and after a period of development, the resulting 5.56mm cartridge was born, mated to the advanced ArmaLite rifle design. The ArmaLite rifle was unlike previous US Army rifles in many ways, perhaps not the least significant of which was the method of its development. Previous Army designs were developed by Army Ordnance, but the ArmaLite rifle was an independent development by a USMC officer-turned-Army Ordnance Colonel and an aircraft design engineer, in the employ of a division of Fairchild, an aircraft manufacturer. The original AR-10 design, in the same full-power caliber as the M14, competed in the light rifle trials, but was unsuccessful due to the exotic composite barrel, which burst during testing. The later AR-15 design, using the basic principles of the AR-10, but adapted for a much smaller .22" caliber cartridge at the request of Army Field Forces Board No. 3. The combination proved wildly successful, and a derivative design, the shorter M4 Carbine, remains the standard infantry weapon of the United States Army today.

Jumping backward in time, The "Kentucky" rifles collectively present an outlier, being much higher velocity and smaller caliber than their contemporaries. This was largely due to their tight rifling and sturdy construction, which incidentally made them unsuitable for use as a standard infantry arm, as they could not be loaded quickly. It did however foreshadow the improvements that would be made to rifle performance as rifling, Minié balls, and breechloading mechanisms allowed rifle-muskets to catch up to their civilian rifled cousins. The "Kentucky" rifles do not represent the state of military small arms at the time, but are included for completeness only.

A very strange anomaly can be seen at the bottom of the table, with both the 16th Century arquebus and 14th Century hand-gonne. Both have higher velocity than the later Charleville musket! Why is this? I do not know for sure, but I suspect that during this period, great emphasis was placed on defeating the personal body armor of the time. To do this would require considerable velocity using the bare lead round ball projectiles of the time. By the 18th century, all that was left of the heavy plate worn by infantry and cuirassiers of the 16th century was the gorget - a decorative neck-guard used as a status symbol. Without the need to penetrate heavy armor, and with no real ability of an individual to hit targets at beyond 20 yards with a smoothbore musket, velocity decreased.

Since the 18th century, the caliber and projectile weight of small arms have progressively decreased, while the muzzle velocity has progressively increased. The change from 7.62mm caliber rifles to 5.56mm caliber rifles follows this trend, and I expect sometime in the future that the 5.56mm caliber will be obsolesced by something even smaller, lighter, and higher velocity.

EDIT: Turns out, by pure serendipity, diving through the Weaponsman archives digs up a very similar article they wrote on the exact same subject a while back. Readers may find it interesting.

Thursday, April 11, 2013

What is a clip? What is not a clip?

You've just gotten into firearms. It's a new, strange world full of opinions, history, and lots of marketing. You and your friend, who's been into guns for ages, it seems, go to the gun store for a look around. You've just bought a Savage Model 64 a few weeks back, and you've had a hard time finding any of the little ugly black aluminum bits that hold the ammunition. You come up to the gun counter, get the attention of a clerk, and ask:

"Hi, you got any clips for a Savage .22?"

The clerk groans and rolls his eyes. You look back at your friend, wondering what you did, and he looks a little embarrassed, but he's making a noble effort to hide it. What went wrong?

Gun owners can be very sensitive about this little quirk of firearm terminology. "Clip" is a flag to many of them that says "I am an idiot; I learned everything I know about firearms from TV, and if you interact with me for any length of time, I will make your day difficult." Sadly, like many people who use the term "clip" to mean "thing you load your gun with", you just want a magazine or two, and to go about your day.

Well, you can't change gun owners. If you could, no one would use lever actions anymore. Nah, we're all a bunch of sticks in the mud, and often pretty loud about it, too. It's better, trust me, to just play along, and learn the difference between a magazine, and a clip.

There are a number of resources online which aim to teach this difference. All the ones I have seen do not quite reach the mark. I will attempt to give the most concise, but widely-applicable definition that I can.

The term "clip" refers to devices made of (usually) a single piece of stamped and/or bent metal which retains rounds ammunition for the purpose of feeding into a weapon or magazine, and which does not contain a spring for advancing the cartridges to the chamber during cycling.

 Sheesh! That was a mouthful! Why does it have to be that way?

Clips, almost always, contain springs. From SKS stripper clips, to revolver moon clips, it's extremely common for clips to be sprung or contain springs. The important distinction here lies in what the spring does. In virtually all clips I'm aware of, the spring acts to hold the rounds in the clip. In a magazine, the mainspring performs two, or even three functions:

1. To hold the rounds in the magazine.

2. To push the next round into the feeding position, after a round has been stripped from the magazine.

3. (often) To hold the magazine together.

To this end, the springs in magazines are usually large, coiled wire springs, which are a separate part. Because of these large, dedicated springs, magazines are usually much, much more expensive than clips.

As if things needed to be more complicated, not all clips are springs, however. This .303 British 5-round clip holds its cartridges in primarily by friction. It is somewhat springy, but if you were to polish the inside of the clip to 400 grit, it probably would not hold the rounds in place any more.

The video by Life, Liberty, Etc claims that "clips are for loading magazines, and magazines are for loading the breech." While this is often true, in many cases it is not. For instance, with revolver moon clips, there is no magazine, and the clip holds ammunition in place while it is seated in the chambers, and merely simplify loading and unloading by making the ammunition a single unit. With a Garand en-bloc clip, the ammunition is loaded into the magazine, but it is the en-bloc clip's feed lips which hold the ammunition in the proper feeding position as it is rammed by the bolt into the chamber. The next round of ammunition is then forced into position by the internal magazine's spring. In this way, the clip and magazine work together as a unit to allow the gun to function.

The above is a lot to remember, for anyone. The Life, Liberty, Etc definition is a bit shorter, but it doesn't really help you if you see some nondescript clip-like object at the gun show and want to know if it's a magazine or a clip. Here's perhaps a more helpful mnemonic:

"Cheap clips, expensive magazines".

Clips are almost always simpler, and thus cheaper than magazines. Often, they are downright disposable. It's not uncommon for someone to spend more than $20 on a single magazine, even for used examples, but you might spend $20 on a bag of 50 clips without being branded a thief. The fact that "cheap" and "clip", and "expensive" and "magazine" have the same number of syllables, respectively, should help the reader remember, in general, which is which.

There are endless permutations to clips and magazines, some (thankfully, very rare) blurring the line between the two. Hopefully, however, this article has given the reader some insight into which is which, and why gun owners are so anal about the difference between the two.

Friday, February 15, 2013

The Cult of Caliber

Nearly every American firearms enthusiast has been to a gun store, a gun show, a gun forum, or some other gun-related venue, and heard:

"Yeah, I don't carry a [gun of X type] that isn't in [a specific caliber, a caliber above X arbitrary value, etc]."

And, if you haven't yet, you will.

What is it about specific calibers, be it .308 or .45 or something else, that really turns people on? After all, it's just a measurement of one particular area on the projectile. A fetish for bullet mass, or better yet cartridge muzzle energy, would make more sense. Yet, there it is.

Today I want to address two specific hymns sung by acolytes of the Cult of Caliber, the first being this:

"If a 5.56 round fails to [tumble/fragment/expand], then what you really have is just a glorified .22."

Variations on this theme appear everywhere, even some well respected defense journals. But something has been bugging me about it.

The first is, isn't this basically the same as saying "if a 5.56 round hits a target and performs exactly like a .22 LR, then it won't be any more effective than a .22 LR"? It may be true, but besides being a bit disingenuous by singling out 5.56, it doesn't really seem useful, as it doesn't tell us anything about how likely it is that 5.56 will perform like a .22.

My other objection is that there's nothing special about a caliber. It's just a measurement, either the diameter from one land to another, the diameter of the grooves, the diameter of the projectile itself, or even just some arbitrary number that's kinda close to one of those measurements. There aren't any caliber-specific performance nodes where one caliber has something special going for it over another.* The statement above frames the situation as if 5.56 has some special quality, that other calibers don't have, which is detrimental to its terminal effectiveness. Even assuming the above statement were true, why would 5.56 be special? Shouldn't the below statement be just as true?

"If a 7.62 round fails to tumble, fragment, or expand, then what you really have is just a glorified .32 ACP."

.32 ACP from a handgun produces about as much energy as .22 LR from a rifle. It's almost certainly not any more effective. How then, even if the oft-heard statement about 5.56 were true, would it inform us about any deficiency in the cartridge? And if it's not true, why take it seriously?

A similar, but different quip is also often heard, relating to 5.56's parental history:

"5.56 is based on the .222 Remington, which was intended as a varmint cartridge."

While it's true that the .222 Remington was and is popular with varmint hunters, the 5.56 was, with some very explicit supporting evidence, designed specifically as a battle cartridge. Indeed, one could as easily say that the 7.62 is just an overgrown varmint cartridge, it being the same caliber as the .32-20, which was a common caliber for small game in previous years. This quip is a bit more banal, and really isn't based on anything but semantics. A chambering isn't good for only one thing; just because the .222 Remington sees a lot of use as a (long range) varmint cartridge doesn't mean that you couldn't easily kill a person with it, or that it's only effective against varmints. Considering the fact that varmints are usually dispatched by blowing gigantic holes in them, a "varmint" cartridge loaded with appropriate bullets might be a real man-stopper.

It's simply not appropriate to judge a cartridge by its caliber alone. Caliber is just a measurement; high velocity bullets are not like icepicks; they do not simply poke a hole of their size and shape, even if they don't do anything exotic. For example, here's a video of a perfectly stable .30 Carbine bullet impacting a block of gelatin and doing some pretty dramatic things to it. This post isn't intended to settle whether 5.56 is a good man-stopper or not once and for all (I was hoping its steady half century of use for that purpose would), but I am hoping I've thoroughly put down those two particular arguments.

*This isn't entirely true, as propensity for yaw actually scales with caliber. Here's a paper describing the phenomenon. However, this assumes homologous bullets, and so you could have a .30 caliber bullet that yaws as easily as a .22 caliber bullet, etc., if they weren't homologous.