Sunday, January 27, 2013

Unusual Firearms: The Gast Gun

During World War I, aerial combat between aircraft happened for the first time in history. It soon became apparent that machine guns were needed on aircraft, because pilots needed to get a large number of rounds on target to score a kill. However, the high rates of fire were also the cause of certain problems. For one, the frequency of jamming increased with the firing rate. Another problem was how to provide adequate cooling for the barrel after firing a large number of bullets. The gun we will study today attempted to solve these problems in an unusual way.

The Gast gun was invented by Karl Gast, a German, during January 1916. He was working for the Vorwerk Company at this time. Karl Gast's solution to the heating and jamming issues was, rather than using one gun, his idea was to combine two barrels and two actions into a single firearm. What was unique about this mechanism was that upon firing one barrel, the recoil was used to load and charge the second barrel. When the second barrel was fired, the recoil would be used to load and charge the first barrel and so on. Each barrel and action were fed by a separate drum magazine.

Side view of a Gast Machine Gun. Click on image to enlarge.

Gast gun seen from the top. Click on image to enlarge.

Each of these drums held 180 rounds of 7.92x57 mm. Mauser rifle cartridges (also known as 8 mm. Mauser -- it is still a popular hunting cartridge even in the 21st century). Because each barrel would fire alternately, this could easily achieve firing rates of 1600 rounds per minute without overheating or jamming issues. The firearm was also designed for ease of maintenance and could be field stripped in about one minute. Even if there were problems with one side of the weapon, it could still fire single shots from the other barrel. It was also easy to change the ammunition drums and an experienced operator could do this within a few seconds.

Karl Gast first demonstrated this weapon to the German military in August 1917 and they were highly impressed by its design and immediately ordered 3000 guns, with the first 100 guns to be delivered by 1st June 1918. They later changed their minds and ordered 6000 more guns by September 1918.

Plans were also made to manufacture a variant that fired 13x92 mm. TuF ammunition with curved box magazines.

Click on image to enlarge.

However, this variation of the Gast gun never reached the production stage. 

While the gun was very successful, it wasn't very widely used and therefore, the Allies had no idea that it even existed by the time World War I ended. They only found out about it in 1921. Incidentally, Karl Gast had also applied for a US patent in 1920 and finally received it in 1923. The US Army got interested in the design and evaluated one. They found it very reliable, but felt that it didn't offer enough of an advantage over their existing machine guns to justify purchasing it.

The Gast gun was not used by the Germans during World War II, but this didn't mean the end of that design. The Soviets borrowed the concept to design their twin-barreled 23 mm. GSh-23 and 30 mm. GSh-30-2 series of autocannons, used on many of their aircraft in the 1960s and 1970s, such as the MiG-21, MiG-23, Sukhoi Su-25, Tupolev Tu-22 and Tu-95, Mi-24 and Mi-35 helicopters etc. A GSh-23 variant is being used in India's new HAL Tejas fighter aircraft in the 21st century, so this innovative design lives on.

Wednesday, January 23, 2013

Powder Flasks

In our previous post about powder horns, we noted that these were containers used to carry black powder. As we noted previously, powder horns are actually made out of animal horns (usually cattle, bison or deer). There are containers made of other materials too, which are called powder flasks. We will study them in this post.

We actually saw one example of a powder flask in our last post:

Indian made Powder Flask. Click on image to enlarge. Public domain image.

The above flask is from India and is made of ivory, with some brass and amber fittings. This flask dates to India's Mughal period. These flasks tended to have fine carvings of animals and hunting scenes, such as the two examples below:

Click on images to enlarge, Public domain images.

The above images show two more Indian powder flasks, made of ivory with brass and amber fittings. Pressing on the brass handle opens the mouth of the carved animal figure and dispenses some powder.

In Europe and America, powder flasks tended to be made of copper, tin or brass, such as the examples below:

Flasks made of brass, tin and copper. Click on images to enlarge

As can be seen by the images above, such flasks were commonly decorated with carved hunting scenes or pretty patterns. Some powder flasks were even made of lacquered wood, coconut shells, bone, leather etc.

Monday, January 21, 2013

Powder Horns

During the early part of firearms history, people were forced to carry separate containers of black powder, bullets and wads, because the self-contained cartridge had not yet been invented. Today, we will study one of the early devices that people used to carry black powder around, the Powder Horn.

Black powder has the property that when it is dry, it stays in powder form and can be poured out easily. If it gets damp, then it forms cakes and wetness also prevents it from burning at all. Hence we have the American saying, "keep your powder dry", which means "be prepared for action". This saying allegedly originated in England with Oliver Cromwell, who allegedly said "Trust in God and keep your powder dry". Whatever the origin, there was a need for firearm users to keep their powder dry and this is why powder horns were invented.

The use of animal horns to carry black powder was mainly due to a few reasons:

  1. Animal horns are naturally waterproof.
  2. Animal horns are naturally hollow inside.
  3. Animal horns are durable and cheaply available (especially cattle and buffalo horn).
  4. Animal horns are non-sparking, unlike iron containers which have the risk of creating a spark when two metal parts strike each other.

Powder Horns. Click on image to enlarge. Public domain image.

The powder horn simply consists of a cattle or buffalo horn with wooden plugs on both ends. The horn is hollow and filled with black powder. To dispense some powder, the user merely removes the plug on the narrow end and pours some powder out into a measuring flask. The horn usually has a rope attached to it so that it may be hung from the user's waist. In some cases, the user would decorate their powder horns with attractive artwork (such as the topmost powder horn in the image above).

Cattle and buffalo horns were used to make powder horns, because they were cheap and readily available. However, these were not the only materials used to make powder horns.

Indian made powder horn. Click on image to enlarge. Public domain image.

In the above image, we see a fine powder horn from Northern India dating back to the 17th century Mughal period. It has high quality carvings depicting various animals on its outside surface. This should strictly not be called a "powder horn", since the material used is not a horn at all. Strictly speaking, this is a powder flask, which we will study about more in the next post. The above container is actually made from elephant ivory, with some amber and brass parts. When the brass spanner handle is depressed, it opens the mouth of the antelope at the end and dispenses powder. The brass spanner also has a loop so that the hunter can easily carry this on his belt.

Once the cartridge was invented, people did not need to carry powder horns any more, as it was more convenient to carry cartridges which already had the powder pre-measured, along with a ball wrapped in it. Hence, the use of powder horns started to decline during the 18th century. These days, the only users of powder horns are history enthusiasts who like to hunt the way that their ancestors did.

Sunday, January 20, 2013

The Puckle Gun

In today's post, we will study an early machine gun: the Puckle Gun. We'd first mentioned this gun many months ago, when we studied the history of revolvers. We will now study this firearm in more detail.

The Puckle gun was invented by a London based lawyer named James Puckle, who had an interest in firearm design. He received a patent for his design in 1718.

Part of the patent application for the Puckle gun. Public domain image.

This was a flintlock firearm fitted with a multishot cylinder, much like a revolver. The cylinders were designed to hold 11 shots at a time. Unlike revolvers, there was a manual crank attached to the back to bring each chamber of the cylinder to the firing position. It was mounted on a tripod and the barrel was about 3 feet (0.91 meters) long. The caliber of this weapon was 1.25 inches (32 mm.). Typical of the era, the firearm came with bullet molds to cast bullets for it (part #21 in the above patent application).

This weapon was supposed to be used as a defensive weapon. If you look at the patent flier sheet above, the weapon is advertised as "A Defence" and the tagline below the title reads: "Defending KING GEORGE your COUNTRY and LAWES / Is Defending YOUR SELVES and PROTESTANT CAUSE". Below the drawing of the gun, it says that it is intended for use in "bridges, breaches, lines and passes, ships, boats, houses and other places."

A very interesting and unusual part of this design are the parts labelled 16 and 17 in the figure above (and also 18 and 19, which show a single chamber of 16 and 17 respectively). It shows the plan of two cylinders used by this rifle. Notice that the shapes of the holes in the two cylinders are different. This is because the gun was designed to fire two different shapes of bullets and the patent document elaborates how they were to be used. The cylinder that fires round bullets was designed to be used against Christian enemies and the cylinder firing square bullets was intended to be used against the Turks, who were Muslim. Apparently the square bullets were considered to be more damaging and the patent document explains that using square bullets against the Turks would 'convince them about the benefits of Christian civilization'! These days, such views would be considered quite inappropriate and racist, but views were a bit different back in the 1700s when this firearm was invented. Incidentally, the square bullets had to be discontinued soon afterwards, because they had a tendency to fly erratically through the air.

Another general point of interest about this patent was that it was written shortly after a change in British Patent law. The new patent law stated that the inventor must describe the invention and how it works in writing, in order to be considered for a patent. This gun's patent documentation was one of the first ones to do it as per the new patent law standards.

While the Puckle gun was an interesting design, it never was a huge success. Part of the problem was that the design had many complicated components and most British gunsmiths didn't have the necessary skill-sets to easily make these parts. Even though it was a commercial failure, the gun was way ahead of its time. It was the precursor to modern machine guns as well as revolvers.

Thursday, January 17, 2013

The Maynard Tape Primer

After all the geeky stuff we've studied in the last few posts, it might be a good idea to study a piece of history instead. We will study the Maynard Tape Primer system in today's post.

First, let us go way back to one of the earliest posts on this blog, which was posted around 2 weeks after this blog started. We're talking about the percussion lock system, which was invented by the Reverend Alexander Forsyth. While he did invent the firing system, it wasn't widely adopted by other manufacturers until the patent rights expired around 1840 or so.

While the percussion lock was a big improvement over the flintlock in that it fired quicker and wasn't as affected by damp weather as a flintlock, reloading was still a slow process, especially for muzzle loading weapons. In the era of single shot firearms, any scheme to reduce the number of steps needed to reload a firearm was definitely a time saver.

The classic percussion cap muzzle loader requires the user to pour some powder down the muzzle, then ram a ball and cloth patch down the barrel, then pull the hammer back and place a copper percussion cap filled with a fulminate (such as mercury fulminate or potassium chlorate) on the nipple, before preparing to fire. Dr. Edward Maynard, a dentist with an interest in firearms design, figured out how to remove one of these steps.

Dr. Maynard's solution was to replace the copper percussion cap with a different system. His idea was to take a thin strip of paper, embed pellets of fulminating materials on it and then glue a second thin strip of paper on top to hold the pellets in place. Then, the paper tape is rolled up and attached to the side of the firearm, near the chamber. Every time the hammer is cocked, a feeding mechanism advances the paper tape so that the next pellet is moved in front of the nipple. When the hammer drops, it not only detonates the pellet, but also cuts the used part of the paper tape.

The Maynard Tape Primer System. Public domain image.

This system was cheaper and quicker to manufacture, since paper is much cheaper and easier to handle than copper. With this system in place, the user would only need to pour in the powder, load the ball and cloth patch and then cock the hammer and the firearm is ready to fire. There is no need to place a percussion cap onto the nipple or cone, which makes the reloading process faster. Dr. Maynard patented this system in 1845 (it was his first firearm patent) and it was used by some commercial manufacturers and attracted the attention of the US government.

The US Army's Ordnance board was initially hesitant about adopting this design, but it got the enthusiastic backing of the then Secretary of War, Mr. Jefferson Davis (who later went on to become the President of the Confederate States of America). Therefore, this mechanism was adopted in the Springfield Model 1855 rifle-musket, which was issued to the US Army. The US government paid Dr. Maynard a royalty of $1.00  for every Model 1855 rifle-musket that was manufactured. If this seems a small amount of money, bear in mind that at that time, the cost of manufacturing the entire Model 1855 musket was $18.00, so this invention made him a very rich man. Dr. Maynard went on to develop various other firearm inventions and registered a total of 23 different firearms related patents during his life.

Springfield Model 1855 musket. Click on image to enlarge. Public domain image.

In the above image, note the dark gray part between the hammer and the nipple, which is the Maynard tape primer system.

So why did we not see this system continue to be used very much afterwards? There were multiple reasons: While the system worked well under clean controlled conditions, it was a different story when used outdoors. British cavalry troops who were armed with Greene carbines (which used the Maynard tape system) during the Crimean war, found them unreliable on the battle field. Tests conducted by the US army in the field between 1859 and 1861 showed that about half the primers misfired and the tape feed springs also didn't work well. The mechanism was also unreliable in muddy conditions and fouled easily. The biggest drawback was that though this system was advertised as waterproof, it didn't actually work well in damp conditions. An attempt was made to use foil instead of paper to make the tapes, in order to solve the problems with damp weather. In spite of this improvement, the Ordnance department dropped the Maynard system and went back to the old percussion cap mechanism with the Springfield Model 1861.

Springfield Model 1855s were used by both sides during the American Civil War, as they were available in greater numbers than the Springfield Model 1861, especially during the beginning of the war

While no real firearms today use the Maynard tape primer system currently, variants of his system are still used for toy roll cap pistols today!

As you can see from the above video, the feed system is somewhat unreliable and doesn't fire on every trigger pull. This and the fact that it is affected by dirt and damp weather spelled the doom for the Maynard Tape Primer in real firearms and only toys use it these days.

Wednesday, January 16, 2013

The Effect of Wind on Ammunition Performance

In our last post, we discussed the effects of air density on ammunition performance. In this post, we will study the effects of wind on performance.

In practical outdoor shooting, especially at longer ranges, there is a good chance that wind may be present and this could affect the ballistics of the bullet. Therefore, it is a good idea to study exactly how it affects bullet trajectory.

The effect of wind on the bullet trajectory depends on the direction of the wind and the speed that it is blowing. It is easy to compensate for wind if it is blowing at a steady rate in a fixed direction. It is much harder to compensate for wind if it is sporadic and blows in gusts of differing velocities. At longer ranges (say 1000 meters), the wind may also blow in different directions along the path to the target.

There are four types of winds we need to concern ourselves with:

  1. Headwind - This is wind that is blowing from the target to us.
  2. Tailwind - This is wind that is blowing from behind us towards the target.
  3. Crosswind - This wind blows from right to left or left to right across the line between the firearm and the target.
  4. Vertical wind - This is usually encountered in mountainous areas and is caused by the wind bouncing off the side of a hill or mountain. This wind moves in a vertical direction (blowing up or down) and pushes the bullet higher or lower on the way to the target.
The first three types of wind are considered to be horizontal winds and the last one is a vertical wind. The headwind and tailwind are easy to account for. Recall that in our previous article, we discussed a term called "drag force", which serves to slow down a bullet horizontally, as it travels through the air. As was discussed in the previous article, drag force is proportional on the velocity of a bullet through the air. Therefore, if a bullet is fired through a headwind, it is moving faster relative to the air than if it were to be fired with no wind. Therefore, this causes an increase in drag forces and the bullet travels slower. Similarly, if a bullet is fired through a tailwind, it is moving slower relative to the air, than if it were to be fired with no wind. Therefore, this causes a decrease in the drag forces and the bullet travels faster. This means that when firing into a headwind, it is necessary to slightly raise the angle of the barrel and when firing into a tailwind, it is necessary to slightly lower the angle of the barrel to compensate.

The famous English author W.W. Greener cites the following formula to calculate how much to compensate for headwinds or tailwinds:
R = V * D/4

R = range distance to compensate by (in yards)
V = velocity of the wind (in miles per hour)
D = distance to the target (in hundreds of yards)

Say we are shooting at a target 300 yards away and there is a tailwind of 10 miles/hour blowing behind us. Then we calculate:
R = 10 * 3/4 = 7.5 yards

This means that if the target is 300 yards away, we should really treat it as though it is 300 - 7.5 = 292.5 yards away and adjust our sights accordingly. If this was a headwind instead of a tailwind, we would treat the sights as though the target was 300 + 7.5 = 307.5 yards away. If you remember our discussion on Minutes of Arc (MOA) from a few months ago, the range adjustment translates to a 1/4 MOA adjustment for this distance (usually one or two clicks on the scope, depending on model). While this seems like a small adjustment amount, the compensation amount increases with distance to target. If we were shooting at 900 yards instead of 300 yards, then the same 10 miles/hour wind will require 1.75 MOAs correction.

A crosswind causes a bullet to move in a large deflection horizontally and also causes a small vertical deflection. A vertical wind causes a large deflection in the vertical direction and a small horizontal deflection. We can easily understand the large deflections, but why are the small deflections caused? The reason for these small deflections is because a spinning bullet tends to turn to face the wind, due to spin stabilization and the resulting torque causes a small deflection.

In reality, we often do not get a true headwind or tailwind, but rather a wind that blows at an angle to the shooter. Therefore, we must break this wind up into (1) headwind or tailwind component (2) crosswind component and (3) vertical wind component. In this case, we must compute the effects of each of these components separately and then add the results in horizontal and vertical directions to figure out how much to compensate for.

Wednesday, January 9, 2013

The Effect of Air Density on Ammunition Performance

A couple of months ago, we'd discussed how temperature affects ammunition performance. In this post, we will study the effect of air density on ammunition.

When a cartridge is fired, the bullet travels through the air and is slowed down by air resistance. This force acting on the bullet is called aerodynamic drag. The equation to compute drag force is:

FD is the drag force
ρ is the density of the air
v is the velocity of the bullet relative to the air
Cd is the the drag coefficient (a dimensionless constant for an object of a given shape)
A is the cross sectional area of the bullet.

As we can see from the above equation, the drag force depends on cross-sectional area of the bullet, the velocity of the bullet and the air density. Of these, we are mainly concerned with the air density in this article. If the air density decreases, the drag forces decrease and therefore the bullet can move faster through the air. If the air density increases, the drag forces on the bullet increase and the bullet slows down quicker. This makes sense as there is less air to slow down the bullet. Air density decreases as we go higher in altitude, this means that bullets travel further when we are at higher altitudes.

At this point, it may be a good idea to introduce a term: ballistic coefficient. Briefly, the ballistic coefficient of a bullet is its ability to resist the aerodynamic drag. The ballistic coefficient of bullets are measured under standard conditions and available from most manufacturers. If the ballistic coefficient at standard conditions is known and the velocity of the bullet and current air density are known, it is possible to predict bullet performance under any conditions.

There are two different standards that ammunition manufacturers use to measure ballistic coefficient. Some use the Standard Metro conditions where the temperature is 59 degrees Fahrenheit, 78% humidity, 29.5275" (750 mm.) of mercury pressure and altitude of sea level. This standard is used by some manufacturers such as Sierra and Hornady. Some other manufacturers, such as Speer and Nosler, use the International Civil Aviation Organization standard (ICAO), which defines the standard conditions to be 59 degrees Fahrenheit, 0% humidity, 29.921" (760 mm.) of mercury pressure and altitude of sea level. The difference between the values of ballistic coefficients obtained by these two standards is less than 2% though.

Air density depends on three factors: air pressure, air temperature and relative humidity. Of these three, relative humidity has the least effect on ballistic coefficient -- the difference between the ballistic coefficient values of a bullet at 1% relative humidity and 100% relative humidity is about 1%. Therefore the effect of relative humidity can be ignored for most practical purposes. The other two factors (i.e.) air pressure and air temperature have much more to do with air density. A decrease in air pressure results in a decrease in air density. On the other hand, a decrease in air temperature results in an increase in air density. However, as we go up in altitude, the decrease in air density due to air pressure is far more than the increase in air density due to the temperature drop. As a result of this, the density of air decreases as we go to higher altitudes.

On the other hand, if we were to stay at the same altitude, but the air temperature decreases (say between summer and winter), then the effect of temperature decrease is an increase in air density and therefore an increase in the drag forces. This is why bullets will slow down faster in winter than in summer and the bullet trajectory changes.

Some bullet manufacturers have handloading manuals that list formulae to recalculate the ballistic coefficient for different air densities. With the aid of a barometer, the formula and a ballistic coefficient under standard conditions, it is possible to calculate the performance at current conditions.

Wednesday, January 2, 2013

Measuring Effectiveness of Cartridges: Hornady Index of Terminal Standards

First, let me wish the faithful readers of this blog a happy 2013.

Continuing our series on measuring effectiveness of cartridges, the next method we will study is another empirical method, this one originates from a cartridge manufacturer. We're talking about the Hornady Manufacturing Company (a well known manufacturer of ammunition and handloading components here in the USA) and the formula in question is the Hornady Index of Terminal Standards, otherwise known as H.I.T.S.

The Hornady Index of Terminal Standards is intended to be a guideline for hunters to compare cartridge and bullet combinations for any hunting situation around the world. The Hornady company has made an online version of the calculator available on their website, for the benefit of hunters. By looking at the Javascript code behind their webpage, it is not too hard to figure out what formula they are using. The formula is essentially:
HITS = (W2 / 7000) * (V/D2) * 1/100

HITS = Hornady Index of Terminal Standards
W = Weight of the bullet in grains.
V = Impact velocity of the bullet in feet/sec.
D = Diameter of the bullet in inches.

The actual formula on their webpage does a bit of rounding here and there, but that doesn't change the result of the formula too much. Hornady claims that the HITS formula factors in bullet weight, sectional density, ballistic coefficient and impact velocity. Hornady then classifies the HITS value calculated by the formula above into one of four different classification types. The classifications are as follows:
H.I.T.S Suitable For
below 500 Small game animals that weigh less than 50 pounds (22.67 kg.)
501-900 For medium-sized game animals weighing between 50 to 300 pounds (22.67 - 136.1 kg.)
Suitable for Antelope, Deer, Black Bear, Caribou etc.
901-1500 Suitable for large and heavy animals which are generally not considered dangerous, weighing
between 300 - 2000 pounds (136.1 - 907.2 kg.)
This list includes elk, moose, red stag, American bison, zebra, kudu, giraffe and other such
African plains game animals. 
over 1500 Suitable for animals that are considered dangerous game i.e. animals that have no problem
stalking the hunter. This would include lions, tigers, leopards etc.

Let's take the same rifle that we considered when we calculated the Thorniley Stopping Power a few articles earlier. We assumed a .30-06 rifle (such as the M1903 Springfield rifle or the M1 Garand rifle) firing a bullet weighing about 180 grains and .308 inch diameter moving at around 2900 feet/sec. Plugging the numbers into the formula above, we have:
HITS = (1802 / 7000) * (2900 / 0.3082) * (1/100) = 1414.957 approximately

Looking at the classification for this HITS value, we see that this value falls in the third category, i.e. it can be used to shoot large and heavy animals that aren't considered dangerous e.g. elk, moose, red stag, zebra, kudu etc. This is similar to the conclusion we reached when we calculated the Thorniley Stopping Power value for this same cartridge/bullet combination.

Note that the HITS values are empirical and Hornady only classifies the HITS value into four different general categories. A HITS value of 800 doesn't mean that it is twice as powerful as a HITS value of 400, for instance. Hornady says that their HITS rating for their own ammunition is based on measuring impact velocities at 100 yards distance for rifle/muzzleloader/shotgun bullets and 50 yards distance for pistols/revolvers.