Saturday, January 24, 2015

All About Scopes - II

In our last post, we looked at some basics of rifle scopes. We will continue our discussion in this post.

As we saw in our last post, there are mainly two types of scopes: the fixed power scope and the variable power scope. The big difference between these two is that the variable scope has adjustable magnification. 

We will now look at how these scopes are specified. Fixed power scopes are usually specified as two numbers separated by x. For instance: 4x32, 12x40 etc. So what do these two numbers mean? The first number is the magnification factor of the scope. Therefore, in a scope marked as "4x32", this means it magnifies the image 4x times (i.e.) the object appears 4 times larger when viewed through the scope, than if it was viewed using just the eye. So what is the second number mean? The second number is the diameter of the objective lens in millimeters. Therefore, in a scope marked as "4x32", this means the objective lens is 32 mm. in diameter. In many cases, the unit of measurement is specified, so instead of "4x32", it may be more clearly specified as "4x32 mm."

A Bushnell 10x40 Fixed Power Scope. Click on the image to enlarge.

In the above image, we have a fixed power 10x40 scope made by Bushnell. What this means is that it has a 10x magnification and the objective lens is 40 mm. in diameter.

Variable power scopes also have similar designations, except that they have three numbers. The first two numbers are separated by a hyphen (-) and the third number is separated by x. For instance: 4-16x42, 6-24x50 etc. The first two numbers indicate the range of magnification power of the scope. Therefore, in a scope marked as "4-16x42", this means that the magnification factor of this scope can be varied between 4x and 16x. The third number indicates the size of the objective lens in millimeters. Therefore, in a scope marked as "4-16x42", the objective lens is 42 mm. in diameter. As with the fixed scopes, sometimes the specification include the unit of measurement as well, so instead of "4-16x42", it may be more clearly specified as "4-16x42 mm."

A variable power 4-16x42 variable power scope made by Nikon. Click on the image to enlarge.

In the above image, we have a Nikon model M-223 scope, which is a 4-16x42 mm. scope. This is the model we studied in our last post, when we were studying the different parts of a scope.

So, a 10x magnification is better than a 4x magnification, right? Not quite. It is true that the object appears a lot larger on a higher magnification scope, but you see less of the surrounding area through the scope. For instance, if you're looking at a herd of deer through a powerful scope, you can probably see the fur very clearly, but you will be unable to tell which particular deer you're looking at, because you can only see a part of a deer's body through the scope. Also, it is very easy to lose sight of a particular deer if it moves off a bit, because the powerful scope only shows a small area at a time. Bear in mind that with a 10x scope, the field of view of an object at 100 yards (90 meters) is about 2 feet (0.66 meters) diameter. With a lower powered scope, you may be able to see both the head and the body of the deer and can tell which one it is in the herd. 

Higher magnification also reduces the brightness of the image. For instance, if you have two scopes, a 4x40 and a 10x40. They both have the same size objective lens (40 mm.), but they have different magnification power 4x and 10x. The image seen through the 4x40 will be brighter than that seen through the 10x40. This has to do with the exit pupil, which we studied about in the last post. The 4x40 scope has an exit pupil of size 10 mm., whereas the 10x40 has an exit pupil of 4 mm. 

Therefore, for general purpose hunting, a scope with magnification in the range of 3x to 10x works fine for many hunters. Some use variable power scopes that work in this range, others are perfectly happy with a 4x or 6x fixed power scope, some even go for lower power, such as 1.5x or 3x, because they don't hunt at longer distances. For long distance shooting, scopes with magnification of 9x to 18x or so are used and anything more than that can only be used for shooting at targets that don't move.

For most soldiers, US military have generally equipped them with fixed power scopes, because soldiers work in stressful environments and a fixed power scope saves them worrying about which magnification factor the scope is currently set at. The US Army, Air Force and Marines use the Trijicon TA31RCO ACOG sight, which uses a 4x32 fixed power scope. The scope has advanced features, such as dual illumination technology provided by fiber optics and tritium

US Marine using his ACOG scope. Click on the image to enlarge. Public domain image.

Most other military forces also do the same thing for their soldiers. For example, Canada's soldiers are equipped with a C79 optical sight which is a 3.4x28 scope, British soldiers have a standard SUSAT L9A1 sight which has a 4x25.5 scope, Steyr AUG rifles (used by Austria and Australia) have a built-in 1.5x scope made by Swarovski (the same people that make luxury glass chandeliers and jewelry).

Canadian C79 Elcan sight. Click on the image to enlarge. Public domain image.

Snipers have also traditionally used fixed power scopes until recently. During World War II, German snipers used 4x fixed power scopes and US snipers used 8x scopes made by Unertl through World War II and the Korean war. By the Vietnam era, 10x fixed power Unertl scopes were in use by the US Marine snipers, although a variable power Redfield 3-9x scope was also tried out. The Unertl model MST-100 which is a 10x42 fixed power scope, remained in US Marines sniper service for quite a while (until about 2007 or so). The US Army snipers used the Leupold Ultra M3A 10x42 mm. scope or the Leupold Mk 4 LR/T M3 10x40 mm. scope until recently as well. In the recent years, US snipers have been experimenting with variable power scopes. For instance, US Marine snipers have been working with the Schmidt & Bender 3-12x50 mm. scope and the US Army snipers have been working with the Leupold Mk 4 3.5-10x40 mm., Leupold Mk 4 M1LR/T 8.5–25×50 mm. and Leupold Mk 4 6.5–20×50 mm. ER/T M5 scopes. Sandia National Labs also recently demonstrated the RAZAR (Rapid Adaptive Zoom for Assault Rifles) technology based on a request from the US military to develop a compact zoom rifle scope.

In our next post, we will look further into some of the technologies inside a scope.


Friday, January 23, 2015

All About Scopes - I

Many months ago, we had studied about rifle scopes briefly, when studying different types of sights. In today's post, we will cover the subject in a bit more detail.

There are two types of telescopes available to shooters:
  1. Fixed Power Scope - These are simpler and have a fixed magnification factor.
  2. Variable Power Scope - These are more complicated and allow the user to adjust the magnification, according to the distance that the target is from the rifle.
To understand more about these two types, let us first look at the main parts of a scope:

A scope made by Nikon.

  1. Eyepiece
  2. Ocular Lens
  3. Exit Pupil
  4. Power Ring
  5. Windage Adjustment Control
  6. Elevation Adjustment Control
  7. Objective Lens
  8. Eye Bell
  9. Objective Bell
  10. Parallax Compensation Control
In the above image, 1 is the eyepiece, which is the end of the scope that the user looks through. The eyepiece encloses a smaller lens, called the ocular lens (2), through which the user views the target. The eye piece generally has a focusing control at the end the sight to obtain a sharp image of the target and the reticle.

The exit pupil (3) is the size of the column of light that comes through the eyepiece: the larger the exit pupil is, the brighter the image. The exit pupil size is defined as the diameter of the objective lens divided by the magnification power of the scope. So, if the diameter of the objective lens is (say) 40 mm. and the scope has 4x magnification, then the exit pupil is 10 mm. For variable power scopes, the magnification can be changed, for instance, from 4x to 10x. This means that, assuming you have the same 40 mm. diameter objective lens as above, the exit pupil will vary from 10 mm. to 4 mm. (i.e.) if you increase the magnification, it will decrease the exit pupil size and vice versa. A smaller exit pupil means the image will appear dimmer and a larger exit pupil means the image will appear brighter. 

The power ring (4) is a feature that is only found on variable power scopes. By turning the power ring, the user can change the magnification power of the scope. This feature is not found in a fixed power scope.

The windage adjustment control (5) allows the user to adjust the scope in the horizontal direction (left or right). The elevation adjustment control (6) allows the user to adjust the scope in the vertical direction (up or down).

The objective lens (7) is the large lens which is further away from the user. This lens concentrates the light that goes through the scope. Larger lenses let more light in and in general, the larger the lens, the higher the magnification power of the scope. Typically, the diameter of the larger lens is measured in millimeters.

The eye bell (8) encloses the eye piece and the objective bell (9) encloses the objective lens. 

Variable power scopes of higher quality have a parallax compensation control (10). Basically, parallax is an optical effect caused by the objective lens not being coincident with the reticle. Therefore, putting the eye at different points behind the ocular lens makes the reticle crosshairs appear on different points on the target, which could cause aiming errors. The parallax compensation control allows the user to adjust for the parallax effect.

Some scopes (both fixed and variable types) also have a brightness control for the scope's reticle, so that the crosshairs can be seen in low light conditions. Some high-end scopes also have a feature called Ballistic Drop Compensation (BDC) which allows the user to adjust for the effect of gravity acting on a bullet (i.e. the amount the bullet drops as it travels a certain distance horizontally).

In addition to all these, we must also define a term which we used above: magnification. This is the ratio of the size of the image as viewed through the scope, compared to if it was viewed by the naked eye. For instance, if the magnification factor is 4x, this means an object appears 4 times larger in the scope than if the object was seen without it.

In the next post, we will study some more details about scopes.


Thursday, January 22, 2015

Are Rifle Calibers Getting Smaller?

In the last 50 years or so, there have been several arguments about the 5.56x45 mm. cartridge and its small bullet. Some argue that the larger bore 7.62x51 mm. cartridge is harder hitting and therefore better. Others argue that the 5.56x45 mm. cartridge is lighter, but hits adequately, therefore a person can carry more of them. This caliber debate has been going on for a while. Bear in mind that in the early 1950s, when the 7.62x51 mm. cartridge was first introduced, several people from that era thought that *it* was a smaller cartridge! This is because it replaced the larger .30-06 cartridge which was in service since about 1906. As we will soon see, the decrease in size of cartridge calibers has actually been going on for a lot longer.

In the early part of the 19th century, soldiers mounted on horses (cavalry) were still an important part of many armies. We hear accounts of several famous cavalry battles, such as the Charge of the Light Brigade (and the lesser known Charge of the Heavy Brigade at the same battle),  Pickett's charge, Battle of Little Bighorn etc. It was the opinion of military experts of that period, that the bore of an infantry musket must be large and the bullet heavy enough, to stop a charging cavalry soldier. It was believed at that time that a smaller bullet, even with greater velocity and equal momentum  compared to a larger bullet, would only wound the foe, but not instantly disable him. However, it was later found by experiment, that the increase in velocity of a bullet makes up for what it loses in mass, and a lighter bullet has greater range and a soldier can carry more of them, which makes the infantry man much more effective in the field. Therefore, since about 1850, as firearm technology gradually started moving towards rifles, the size of bullets have been decreasing with every advance in infantry weapon technology. The following table is largely transcribed from The Gun and its Development by W.W. Greener and lists the diameters of bullets from various military forces in Europe and America from 1850.

Year Country Firearm Caliber
1850EnglandBrown Bess (11 bore).750 inch (19.2 mm.)
1850EnglandBrown Bess (14 bore).693 inch (17.85 mm.)
1852EnglandEnfield.577 inch (14.8 mm.)
1854Austria28-bore rifle.550 inch (13.8 mm.)
1860Sweden40-bore rifle.488 inch (12.6 mm.)
1866France59-bore rifle.433 inch (11.0 mm.)
1867Austria62-bore rifle.420 inch (10.7 mm.)
1869Switzerland75-bore rifle.400 inch (10.4 mm.)
1871Germany, Spain and Holland58-bore rifle.433 inch (11.0 mm.)
1871England51-bore rifle.450 inch (11.43 mm.)
1874France58-bore rifle.433 inch (11.0 mm.)
1878Sweden76-bore rifle.396 inch (10.15 mm.)
1880Serbia76-bore rifle.396 inch (10.15 mm.)
1886France and Portugal150-bore rifle.315 inch (8.0 mm.)
1887Turkey.350 inch (9.5 mm.)
1887EnglandEnfield Martini.400 inch (10.25 mm.)
1888Germany156-bore rifle.311 inch (7.9 mm.)
1888Germany150-bore rifle.315 inch (8.0 mm.)
1889England172-bore rifle.303 inch (7.7 mm.)
1889Belgium173-bore rifle.303 inch (7.65 mm.)
1889Denmark150-bore rifle.315 inch (8.0 mm.)
1891Switzerland.295 inch (7.5 mm.)
1891Italy.256 inch (6.5 mm.)
1891Russia.300 inch (7.62 mm.)
1892Spain.276 inch (7.0 mm.)
1892Holland and Romania.256 inch (6.5 mm.)
1893USA.300 inch (7.62 mm.)
1895USA (US Navy only).236 inch (5.87 mm.)

As can be seen in the table, the diameter and size of the bullets has been decreasing for quite a while. As propellants improved and black-powder began to be replaced by more powerful smokeless powders, the sizes and weights of the bullets began to decrease as well.

Tuesday, January 6, 2015

Differences Between the VZ-58 and the AK

First, I'd like to wish all the readers of this blog a very happy 2015.

Quick, identify the firearm in the image below:

Click on the image to enlarge. Public domain image.

If you said something along the lines of "AK-47" or "AKM", then you're wrong. What you're looking at is the Czechoslovakian vz. 58 rifle. The vz. 58 does resemble an AK-47 or an AKM externally, but there are a lot of differences underneath the hood. We will study more about this rifle in this post.

The name "vz. 58" is actually a contraction of "vzor 58' (i,e. "model 58"). The official full name of this weapon is "7,62 mm samopal vzor 58" (i.e. 7.62 mm. automatic firearm model 58"). The number 58 is because this weapon entered service in the year 1958 (the AK-47 is named similarly -- it first entered service in 1947).

After World War II, the Soviet Union started using the 7.62x39 mm. cartridge for its AK-47 and AKM rifles and insisted that all the Warsaw Pact countries use the same cartridge for standardization. Many of the Warsaw pact countries (Poland, Hungary, Romania etc.) adopted the cartridge as well as the AK rifle for their military forces, but the Czechoslovakians decided to only adopt the cartridge, but use their own rifle technologies. They already had a history of developing firearms for 300 years or so, and the city of Brno was most recently known for developing the precursor to the famous Bren gun of World War II. A designer named Jiri Cermak was assigned to develop the new rifle in Brno in 1956 and the new rifle entered service in 1958.

The new rifle was chambered to use the 7.62x39 mm. cartridge, the same as the AK-47. This is about where the similarity between the two ends. What are some of the major differences?

  • Action: The AK-47 (and AKM and the rest of the AK family) uses the long stroke piston system, whereas the vz. 58 uses the short stroke piston system. In the short-stroke system, the piston moves for a very short distance (in the case of a vz. 58, it moves 19 mm. (or about 0.74 inches)), whereupon it is stopped by a projection. The short backward movement of the piston imparts a sharp blow to the bolt-carrier, which separates from the piston and then continues backwards due to momentum. In a long stroke system, the piston and the bolt carrier move backward together. This means that the short stroke piston system has a smaller mass of moving parts, since the bolt-carrier weighs less than the combined bolt-carrier and piston together. Therefore, there is less vibration and balance shift due to the moving parts and the vz. 58 is easier to keep pointed to the target.
  • Firing mechanism: The AK-47 uses a traditional rotating hammer mechanism, whereas the vz. 58 is striker fired.
  • Safety/Fire selector lever: The easiest way to tell if a rifle is a vz.58 or an AK is by looking at the fire-selector lever. The AK-47 family is famous for its clunky large fire selector lever, which is located on the right side of the weapon above the trigger and is cumbersome to operate. The user needs to take the firing hand off the pistol grip to manipulate an AK fire selector lever. The vz. 58 has a smaller, much more ergonomic selector mechanism and the lever can be manipulated without taking the hand off the pistol grip. The following two pictures show the differences (click on the images to enlarge -- the fire selector levers are enclosed in red ovals in the images below):
AKM fire selector lever. Note the length of the fire selector lever and its position relative to the pistol grip.
Click on the image to enlarge.

vz.58 fire selector lever. Notice how it is positioned close to the pistol grip and can be easily manipulated.
Click on the image to enlarge
  • Magazine: The AK-47, AKM and vz. 58 all come with 30 round box magazines, however, the vz. 58 magazine is shaped a bit  differently, so it cannot be inserted into an AK and vice-versa. The vz. 58 magazine is also made of a lightweight aluminum alloy and therefore, it is lighter than the steel magazines of the AK family. The vz. 58 magazine can also be loaded via stripper clips, without removing the magazine from the rifle.
  • Receiver: The early AK-47 receivers were made of milled steel, until the Soviets mastered the art of producing stamped steel parts from the Germans and the AKM (and all subsequent AK models) all have stamped steel parts. This was done to improve the production rate. The vz. 58 still uses a milled steel receiver. While it takes longer to make a milled steel receiver, it is more rigid and therefore has a bit more accuracy.
  • Lock action: The vz. 58 has a tilting lock action with a falling breechblock (similar to Beretta 92)
  • Bolt hold-open feature: When the last round has been fired in a vz. 58, the bolt catch locks the bolt carrier to the rear of the gun and it stays open, which alerts the user that the firearm is empty. In an AK, the majority of the magazines allow the bolt to go forward on an empty magazine, therefore, the user cannot easily tell that the rifle is empty.
  • Stock: The early vz. 58s were made using beech wood stocks, but they soon switched to using a wood-impregnated plastic stock. If you click on the image of the rifle above to enlarge it, you'll notice that the stock has a somewhat grainy look to it. These stocks are affectionately known as "beaver barf" to collectors and are light, durable and economical. AK rifles use laminated wood stocks (earlier models used normal wood and later models use plastic), which are also durable and cheap to produce, but they are a bit heavier. Later stocks on vz. 58 were made of steel and alloys and designed to be foldable or collapsible. One more difference is that the stock on a vz. 58 is designed to be modular and easily detachable/interchangeable.
  • Dust Cover: The receiver on a vz. 58 has no ejection port dust cover, because the receiver is completely enclosed by the bolt carrier. Therefore, the ejection port is huge compared to an AK. This can be easily seen when the rifle is being operated. 
  • Disassembly: The vz. 58 is held by two pins and is designed to be disassembled without using any tools.
Even though the AK family and the vz, 58 look very similar externally, the vz. 58 cannot exchange parts with the AK family because of the vast differences in the mechanisms.

The following video makes the differences between the two very clear.


The vz.58 was manufactured between 1958 and 1984 and around one million rifles were manufactured, which means they are not as widespread as the AK family. They still remain in use with Czech and Slovak military forces, and they were exported to some other countries as well (Cuba, Vietnam, India, Indonesia, Ethiopia, Uganda etc.)

Thursday, December 25, 2014

Pocket Rifles

In today's post, we will study a particular class of firearm that was very uniquely American and popular from the end of the Civil War to the beginning of World War I. We are going to study about Pocket Rifles, otherwise called Bicycle Rifles.

The origin on these weapons has to do with the Stevens Arms and Tools Company, founded by Joshua Stevens. He was a well-respected toolmaker, who had worked for Colt, Eli Whitney, Smith & Wesson, Allen and many other American gunmakers of the era, before founding his own firearms company in 1864. The company's first two models were a Pocket Pistol and a Vest Pocket Pistol (a year ahead of Remington's Vest Pocket Pistol model). In 1869, the company produced what it called a "Pocket Rifle". This was largely based on their Pocket Pistol model, except that it had a longer barrel, better sights and a cap on the pistol's grip to accept a detachable shoulder stock made of wire. Like the Pocket Pistol, the Pocket Rifle was also a single shot model.

In 1872, a larger 'New Model Pocket Rifle' was added to handle cartridges up to .32 caliber rimfire cartridge. Shortly after that, a line called the 'Hunters Pet Pocket Rifle' was also introduced that went up to .44 caliber. The shoulder stock was also modified so that it slid into a dovetail cut into the butt of the pistol and a screw on the backstrap.

Public domain image of Stevens Pocket Rifles

Click on the image to enlarge. Public domain image.

The New Model Pocket Rifle (First Issue) was the same basic design as the Old Model Pocket Rifle, but was larger and had a heavier barrel to handle the bigger .32 caliber rimfire cartridge. It became far more popular than the old model and outsold it by a wide margin. It was only manufactured for three years though, between 1872-1875, after which it was replaced by the New Model Pocket Rifle (Second Issue) model, which was sold from 1875-1896

The second issue model mounted the firing pin in the frame rather than the hammer, as a safety feature. In 1887, a version that fired the .22 Long Rifle (also known as .22 LR) rimfire cartridge was manufactured for the first time. The .22 LR cartridge was also invented by the Stevens Arms and Tools Company and is still the most popular cartridge in the world today (almost every major firearm manufacturer in the world has made at least one product that fires .22 LR). 

When separated into two pieces (the pocket rifle and the stock), each piece measured between 18 to 24 inches (46-61cm.), which meant they could be stowed in a long coat pocket. Weight of the larger caliber models was around 5 to 5.75 lbs. (2.2 - 2.6 kg.) and the lighter models up to .32 caliber only weighed about 2 - 2.75 lbs. (0.9-1.25 kg.) The barrels were offered in a variety of lengths: 10 inches, 12 inches, 15 inches or 18 inches (25 cm., 30 cm., 38 cm. or 46 cm.)

In the 1880s, advertisements for these guns started to refer to them as "Bicycle Rifles", probably as a marketing tactic to sell them to cyclists of that era, as a light rifle that could be carried for self defense.

An advertisement for a Stevens Bicycle Rifle. Click on the image to enlarge.

They were also offered with carrying cases made of leather or canvas and marketed to hunters as a secondary light rifle, and to fishermen to carry with their fishing equipment.

The nice thing about these compact rifles was that they offered much more range and accuracy than pistols, but were much cheaper than other single shot rifles of that era, while also being much more portable than other rifle models. One Mr. A.C. Gould reported that using a model firing .22 caliber cartridges with an 18 inch barrel, ten shots were placed into a target of 8 inches diameter at 200 yards distance.

After the success of the initial models, other manufacturers also started to make pocket rifles, but Stevens continued to dominate the market until the last model was manufactured during World War I. It must be noted that practically all dealer catalogs of that period that advertised pocket rifles. invariably showed the Stevens brand name. Some larger dealers offered pocket rifles under their own brand, but many of these were actually manufactured by Stevens and marked with the dealer's brand name.

While pocket rifles sold very well in America, they remained a very American invention and never really spread to other countries. While they were light and relatively portable, they were all single-shot models. Their popularity began to decline after semi-automatic and fully-automatic weapons became more common.

Tuesday, December 16, 2014

What's the deal with Barrel Shrouds?

So what is a barrel shroud? It is simply a hollow covering tube that surrounds a barrel (either partially or fully). What does it do? Well, it protects the user of the firearm from accidentally burning himself or herself with the hot barrel.

A typical barrel shroud

A barrel shroud typically has many holes throughout its length. The holes serve to reduce its weight and also dissipate heat by venting out hot air. The next picture shows a barrel shroud attached to a rifle.


As you can see in the above image, the barrel shroud is simply that tube with holes that surrounds the barrel. In the above example, the user has also attached an extra hand grip to the barrel shroud. Since much of the barrel shroud is not in contact with the hot barrel, if the user was to accidentally touch the front of the firearm, the user will not get burned by the barrel.



The curious reader is probably thinking now, "isn't that what the stock of a firearm is designed to do?", Yes, the stock and the receiver do protect the user's hands as well, but they are not considered as barrel shrouds, because they serve other purposes as well, whereas the barrel shroud is a separate component that is screwed on around the barrel and explicitly designed to protect the user's hands (or other body parts) from heat.

Barrel shrouds are generally commonly seen with air-cooled machine guns, but they are also optional components for many semi-automatic models. Some shotguns also feature barrel shrouds. There are many third party component makers that make barrel shrouds for various rifle and shotgun models. In general, they are useful to have with weapons that fire rapidly, because the barrel can heat up quite a bit after a few shots in rapid succession.

If a barrel shroud is simply a covering tube to protect a user from touching a hotter part of the gun, then what's the big deal about them? Well, for a while, barrel shrouds were targets of legislative restrictions in the United States. The now expired Federal Assault Weapons Ban explicitly included barrel shrouds in its list of features for which a semi-automatic firearm could be banned (if a firearm had two features in the list, it could be banned under this law). After the law expired, proposals were made to renew the ban, including this provision, but have not been successful so far.

Amusingly, during an interview on MSNBC in 2007, Representative Carolyn McCarthy was asked about her gun control legislation and why it prohibited people from purchasing firearms that have barrel shrouds and if she even knew what a barrel shroud was. After attempting to avoid the questions twice, she finally admitted, "I don't know what it is, I think it is a shoulder thing that goes up!"


It is amazing that she was trying to introduce a law to ban something without even knowing what it was!

Sunday, December 14, 2014

Forging Rifle Barrel Blanks in the 1920s - II

In our last post, we studied some parts of a factory designed to produce rifle barrel blanks. In today's post, we will continue studying the process. As noted before, some of the details come from a book, "The Working of Steel" by Fred Colvin and K.A. Juthe, and in addition, K.A. Juthe was the designer of the factory as well.

Where we last left off, the barrel blanks were straightened out and tested for straightness. The next process was to heat treat the barrel blanks and increase their hardness. We will discuss this heat treating process shortly.

The last process was to grind the ends of each blank and then grind a spot on the enlarged end of each blank and test the hardness of the blank on a Brinell machine, to ensure that the blanks met the required hardness nunbers

The Brinell hardness test was invented by Swedish engineer Johan Brinell in 1900. It was one of the first standardized hardness tests used in engineering and is still used today. The test is very simple. It uses a steel or tungsten carbide ball of diameter 10 mm. (0.39 inches), which is used as an indenter. The ball is placed on the surface of the object to be tested and a 3000 kg. (or 6600 lbf.) test force is applied to the ball for a specific time (normally 10 to 15 seconds). After this, the ball is removed and it leaves a round indentation on the surface of the object. The diameter of this indentation is measured and the Brinell Hardness Number (BHN) is calculated, based upon the diameter of the ball, diameter of the indentation and the force applied to the ball. For softer materials, such as aluminum, a smaller test force (e.g. 500 kg. (or 1100 lbf.) is used instead.


The above image shows a line drawing of the concept and the formula actually used to calculate the Brinell Hardness Number (HB in the image above).

Returning back to our study of the factory process, the barrel blanks were tested for hardness to make sure that they had a Brinell Hardness Number (BHN) of at least 240.


At this point, the barrel blanks were shipped off to a barrel manufacturer, who would then drill, ream, finish-turn and rifle the blanks into complete barrels.

Now. all through the description of the process so far, we've been talking about heating the blanks for various purposes. We will cover the heat treatments in detail here. There were actually four separate heat treatments done to the blanks.

  1. Heating and soaking the steel above the critical temperature and quenching it in oil, to harden the steel through to the center of the blanks.
  2. Reheating the steel for drawing of temper  for the purpose of meeting the physical specifications of the blank
  3. Reheating the blanks to meet the machineability test for production purposes
  4. Reheating to straighten out the blanks when hot.
We will study each of the four heating processes in detail. 

For the first heating process, the blanks were slowly brought up to the required heat, which is about 150 degrees Fahrenheit (65.5 degrees centigrade) above the critical temperature of the steel. The blanks were then soaked at a high heat for about one hour before quenching in oil. The purpose of this treatment was to eliminate any strains already existing in the bars that may have been put there from milling operations done to the bars. Remember that steel is an elastic substance and working it puts stress on the bars. For instance, during the production of steel, the manufacturer rolls the bars through various rollers to make them the required diameter, which causes the bars to come out stressed. The heat treatment process removed the stress caused by rolling, hammering, cutting etc. It also ensured that the heat treatment applied to the entire cross-section of the bar and not just the surface. In addition, if a blank had seams or slight flaws, these opened up drastically during the quenching process and made it easy to determine if a blank was defective or not.

The oil used for quenching was kept at a temperature of  around 100 degrees fahrenheit (38 degrees centigrade). This is an ideal temperature is to prevent shock to the steel when it is dropped into the quenching oil, otherwise it could develop surface cracks on the piece.

The second heating process (the one for drawing the temper of the steel) was a very critical operation and had to be done carefully. The steel had to be kept heated within 10 degrees of temperature fluctuation in the process. The degree of heat necessary for this operation depended entirely on analyzing the steel. Even if the steel was purchased from the same manufacturer, there was always some variation in different batches received from the manufacturer.

The third heating process (reheating for machineability) was done at a temperature of around 100 degrees Fahrenheit (38 degrees centigrade) less than the drawing temperature used for the second heating process. However, the time of soaking was almost double that of the second process.

For both the second and third heating process, after the heating was done. the blanks were buried in lime so that they would be out of contact with air, until their temperature had dropped down to room temperature.

The fourth heating process was used when straightening the blanks. In this process, the blanks were first heated to about 900-1000 degrees Fahrenheit (482-538 degrees centigrade) in an automatic furnace for 2 hours before straightening them. The purpose of heating before the straightening was to prevent any stresses being put into the blanks during the straightening operation. This is necessary because when later processes such as drilling, turning and rifling are done to the blanks, they have a tendency to spring back into the shape they were in when they left the quenching bath. By heating before straightening, the blanks are prevented from doing this.

Another method was later found to produce an even better barrel blank. The blanks were first rough-turned to the final barrel diameter and then heated to about 1000 degrees Fahrenheit (538 degrees centigrade) for about 4 hours before sending them to the barrel manufacturer. Blanks produced with this method remained practically straight during the different barrel making operations (drilling, reaming, finish-turning and rifling). This meant that the barrel manufacturers didn't need to straighten barrels after they were finished (which was a much more expensive operation). This method was tested out with one of the largest barrel manufacturers in the US and it proved to be very effective.

As the reader might be wondering, all this heat-treating needed a large amount of oil for cooling and one of the problems was how to keep all this oil at the proper temperature. After much study, a cooling system was developed for the factory. The next two images show the cooling system as seen on the roof from the outside of the factory.


Click on the images to enlarge. Public domain images.


The next image shows the details of the cooling system:


The hot oil is pumped up from the quenching tanks through the pipe A into the tank B, From here, the oil runs down onto the separators C, which break the oil up into fine particles, that are blown upwards by the fans D. The spray of oil particles is blown up into the cooling tower E, which contains banks of cooling pipes and baffles F. Cold water is pumped through the inside of the pipes. The spray of oil particles collects on the outside of the cold pipes and forms larger drops, which fall downwards onto the curved plates G and then run back to the oil-storage tank below ground. The water pumped through the cooling pipes comes from 10 natural artesian wells at a rate of 60 gallons per minute and this serves to cool about 90 gallons of oil per minute, lowering it from a temperature of about 130-140 degrees Fahrenheit to about 100 degrees Fahrenheit. The water comes out of the wells at an average temperature of 52 degrees Fahrenheit. The pump is driven by a 7.5 HP motor and the speed can be varied to suit the amount of oil to be cooled. The plant was designed to handle up to 300 gallons of oil per minute.

The finished blanks from this factory were sent to different barrel manufacturers to drill, ream, rifle etc. to their requirements.