Corrosive Ammunition

Many months ago, we talked about the development of the percussion lock. This was where the idea of striking a shock-sensitive substance with a hammer to ignite the main charge of propellant was originally developed. In that article, we had mentioned that mercury fulminate was originally used as the primer and was later replaced by potassium chlorate. This idea of using a shock sensitive priming material is still used in today's centerfire cartridges. However, there were some issues with using such primer materials and we'll study about them in this post.

In our discussion about the percussion lock previously, we'd mentioned that the inventor (the Rev. Alexander Forsyth) had used mercury fulminates to set off the main charge. Mercury fulminates continued to be used in priming caps for early centerfire cartridges as well, into the end of the 19th century. However, when people started to switch to using smokeless powders, they began to discover the downsides of mercury fulminate. One of the issues was that mercury fulminate tended to degrade when kept in storage. This was not really an issue when using black powder cartridges, because black powder ignites a lot easier than smokeless powders. However, once people started to switch to smokeless powders for extra power, they found that keeping the cartridges in storage would cause the mercury fulminate primers to degrade so much that they could not reliably ignite the smokeless powder, causing misfires and hang fires. One more problem with mercury fulminates was that in conjunction with smokeless powders, it tended to form copper and zinc amalgams in the brass cases of cartridges, thereby making them unsuitable for reloading.

Due to this, the US Army switched to using potassium chlorate primers in 1898. Some other manufacturers used sodium chlorate instead. While these primers did not degrade as much as mercury fulminate, there were some other problems that came with them. When fired, these primers would decompose and leave a residue of potassium chloride (or sodium chloride) behind in the barrel. Those of you who remember your chemistry lessons in school might remember that sodium chloride is the scientific name for common salt. Potassium chloride is also another corrosive salt. These salts are highly hygroscopic (i.e.) they tend to attract water, especially when in humid conditions. Guess what happens when you have salt and water applied to an iron or steel surface -- that's right, it rusts. Therefore, if the barrel and action are not cleaned after firing such cartridges, there's a good chance that they could rust soon after. Swabbing the surfaces with oil will not prevent these salts from attracting water and rusting the metal.

As a result of this, primers using non-corrosive chemicals were developed in the 1920s, but these were generally used in civilian ammunition only, as the early non-corrosive primers did not last as well in storage as corrosive primers. Due to this, military ammunition tended to use corrosive primers and this was indeed the case for US military ammunition until the 1950s or so. Some other countries (e.g. former Soviet Union, China, Yugoslavia, Bulgaria etc.) continued to use corrosive primers in their cartridges for much longer than this, well into the 1970s and 1980s. Therefore, depending on the source and the age of the ammunition, the user must be wary lest the ammunition is corrosive.

So how does a user ensure that his firearm doesn't rust after using corrosive ammunition. The good news is that this is fairly easy to handle. It turns out that these corrosive salts dissolve in water. Therefore, cleaning the firearm thoroughly using water or a water based lubricant should do the trick. Some people use hot soapy water, others use plain water, still others swear by windex glass cleaner (which is largely water based). After washing off the residue, the firearm should then be dried, then cleaned with normal bore cleaning solution and oiled, as per the normal cleaning procedures.

The firearm should be thoroughly cleaned as soon as possible after firing the corrosive ammunition, to ensure that the corrosive chemicals are removed before they can damage the firearm. While this may seem like a bit of extra work, it is well worth it because there is no way to restore a barrel or chamber back to perfect condition, once it has started to rust. Therefore, the user should go through the extra effort if the ammunition is suspected to use corrosive primers.

As it turns out, the price of surplus ammunition using corrosive primers is often much lower than other types and it is also widely available in the market. So how does a user identify if the ammunition is corrosive or not? One way is by looking at the markings on the cartridges and the manufacturer of the ammunition. For instance, if it is surplus ammunition from certain countries such as the former Soviet Union, Yugoslavia or China, there is a good chance it uses corrosive primers, especially if it is manufactured before the 1980s. US-made ammunition has markings that can give a good clue as to whether the primers are corrosive or not. In case of doubt, there's an easy way to find this out. The user can take a cartridge, pull out the bullet from the front and empty out the powder from the cartridge and only leave the primer behind. Then. the user fires the empty cartridge onto a mild steel plate from a distance of about 1 inch from the muzzle, so that the primer chemicals are deposited on the plate. The user also fires another primer that is known to be non-corrosive onto another section of the steel plate. After firing the two cartridges, the user cleans the firearm as detailed in the procedure above, in case the suspect ammo is indeed corrosive. Then the user simply keeps the steel plate in a warm humid area for a few days. If the section where the suspect primer is fired over shows substantial rusting, then it uses corrosive chemicals.

Another way is to use bright common nails (which are nails made of mild steel with no coating) and pop a primers over one of these nails. If the nail rusts within a couple of days, then the primer is corrosive. The following video shows how this is done, using simple household tools:

Interestingly, the box of suspect ammunition actually says that it is non-corrosive on the box, but it turns out to be corrosive after all. Happy viewing!

What the heck is an "Arshin"?

Imagine you are now the proud owner of a classic Russian Mosin-Nagant M-91 rifle and are excited to try it out for the first time. So you take it out to the range, adjust the iron sights for a target 400 meters away and shoot at it. Upon shooting a few times, you examine the target and notice that you're not hitting where you're aiming at. Is there something wrong with the rifle? Actually, the answer may have to do with your misunderstanding about how the sight works.

A Konovalov type Mosin-Nagant adjustable iron sight.

In the above image, we see a Mosin-Nagant rifle sight called the Konovalov type. This sight acts as both a  tangent sight (for shorter ranges, marked as 4-12) and a ladder sight (for longer ranges, marked as 13-32). Note that the sight is sort of curved, as seen in the first image. Older Mosin Nagants have a flat shaped sight using the same idea.

The mistake that some people make is assume that these settings are in meters (e.g. 4 = 400 meters, 6 = 600 meters etc.) For Mosin-Nagants manufactured before 1930, this is not true -- in fact, these are calibrated in a unit called "Arshin" (plural: "Arshins" in English, "Arshiny" in Russian). So what the heck is an "Arshin" then?

To answer this question, we must go back to 16th century Russia, where this unit of length first originated. This unit was the Russian equivalent of the English "yard" measurement. Its actual length varied over the years, until Peter the Great standardized it in the 18th century to be about 27.95 inches long (or about 71.1 cm. or 0.78 yards). This continued to be how distances were measured in Russia until some time in 1925, when the Soviet Union officially adopted the metric system throughout the country. Konovalov type sights calibrated in arshins continued to be manufactured for some years after, until 1929.

Therefore, with older Mosin-Nagant rifles built before 1930, the sights were actually calibrated in arshins. Hence, when the slider is pushed to 4, the sights are set to aim at a distance of 400 arshins, not 400 meters. 400 arshins is approximately 285 meters, which explains why the rifle might not be shooting where the user expects it to!

Edit: The editor is indebted to Mr. Bernard Samartsev for his comments and corrections to the original article noted below.

The Greener Police Shotgun

The topic of today's study will be an unusual firearm, the Greener police shotgun.

The history of this unusual firearm dates back to shortly after World War I, when the British ruled over very large portions of the planet and the sun never set on the British empire. In several colonies around the globe, the British set up police forces employing locals to handle ordinary law and order issues, with British army garrisons to put down major rebellions and uprisings. There came a need to equip the local police forces of countries like Egypt, India, Hong Kong etc., with weapons to put down riots and jail escape attempts, without the need to involve the local army garrison. Therefore, the British government issued a specification for a new firearm for these police forces.

The requirements of this new firearm type were a bit unusual. First, many of these police forces were not well trained or educated, therefore the firearms had to be extremely simple, sturdy and reliable. They were expected to need minimal maintenance. Since there was a chance that the guns could be used against the British troops themselves, the guns had to be short-range weapons and single-shot only. Another request was that the cartridges used for these firearms should not be easily available. That way, if the police forces decided to rebel themselves, the British garrison could easily take them on.

Greener police shotgun. Click on image to enlarge.

With these requirements in mind, the firm of W.W. Greener, a well known manufacturer of firearms from Birmingham, UK, came up with the Greener police shotgun. The action chosen for this firearm was the Greener improved Martini action that we studied a couple of years ago. This reliable action was known for its simplicity and ruggedness. It was in the Martini-Henry rifle since 1871 and the Martini-Henry rifle was already used by many local militaries, which meant that many locals would be familiar with it. In addition, the barrel, springs and action were made of heavy-duty steel for extra strength and durability. The wood stock extended all the way to the end of the barrel, to prevent damage to the barrel. In addition, note the solid steel nose cap at the muzzle end of the barrel in the picture above. This cap served as extra protection for the end of the muzzle, so even if the gun was placed vertically with the muzzle-end on the floor, the steel cap kept the barrel about 1/4" off the floor. In addition, a bayonet could be attached to the steel cap. The butt-end of the stock also had a steel plate at the end, so it could be used as a club. The stock also had a compartment to store cleaning tools. The barrel of this shotgun had no rifling, so it could only be used as a short range weapon and since it used the Martini action, the user would have to manually unload and reload a new cartridge, each time he desired to fire it. The cartridge that this shotgun was designed to fire was a proprietary 14-gauge shell manufactured by Kynoch Ltd.

The original Mark-I model of this shotgun was released in 1921, mainly to colonial police forces in Egypt. However, it was soon discovered that unauthorized users could use a smaller commonly available 16-gauge cartridge in this gun and stuff the extra space with paper. In response to this, Greener released the Mark-III model shotgun, which had some improvements to prevent this:

New improved cartridge for the Greener Police Shotgun Mark III

In this newer model, the shotgun chamber was altered to take an unusual shaped cartridge. The base of the cartridge was the same diameter as a 12 gauge cartridge, but the front of it was narrowed down to 14 gauge. With an unusual bottle-necked cartridge shape like this, this cartridge could not be used with any other firearm.

In addition, the striker of the shotgun was also modified so that it could only be used with these unusual cartridges. Instead of a normal needle shaped striker, the new striker on this shotgun was shaped like a trident, with the outer two prongs longer than the middle prong. Note that the base of the new cartridge has a deep circular groove around the primer cap. The reason for this groove is so that the two outer prongs fit into the groove and the shorter middle prong can strike the primer of the cartridge. Therefore, the Mark-III shotgun could not use any other ammunition, except for this type of cartridge. If any other cartridge was used, the two longer outer prongs of the striker would strike the base of the cartridge first and prevent the shorter middle prong from striking the primer.

The end result of this was a cartridge that could not be used on any other firearm and a shotgun that could only fire a particular cartridge type. The British authorities were very careful to issue these cartridges in very limited numbers (about two or three per person). Therefore, if criminals stole these weapons or if the local government revolted, these guns would be useful only while the ammunition was available for them.

A lot of these shotguns were issued to colonial police forces in Egypt, Malaya, Hong Kong etc. Some of them were imported into the US in the 1930s, to be used in prisons. Greener continued to manufacture these shotguns even after British colonial rule ended in many parts of the world, until about 1975 or so. Used examples can be found on sale even today.

The Boys Anti-tank Rifle

In our last post, we studied the world's first anti-tank rifle, the Mauser T-Gewehr M1918, which was invented by the Germans. Today, we will study the history of another anti-tank rifle, the British Boys Anti-tank Rifle.

In the last post, we studied that the Mauser T-Gewehr was invented by the Germans because they didn't have any tanks of their own during World War I and had to come up with some solution to counter British and French tanks. Although tank armor had become thick enough to resist the Mauser by the end of World War I, the idea of an anti-tank rifle did not go away.

In 1934, the British decided to design a weapon that could penetrate light armor. The project was originally called Stanchion and was given to the Royal Small Arms Factory of Enfield, Middlesex, England to design. The chief designer of this project was a Captain H.C. Boys.

Captain Boys intended the rifle to be a bolt-action large bore rifle, capable of penetrating light armor, but light enough to be carried by a single person. He looked at the existing rifle cartridges of the day. The 30-06 and the .303 cartridges were found to be too weak (even the armor-piercing variants). The US made Browning .50 BMG cartridge was found to have some potential, because it could penetrate 3/4" armor at 100 yards, but they wanted something a bit more powerful than the .50 caliber cartridge. Therefore, they started with a Browning .50 caliber cartridge case, widened the case's neck to accept a .55 caliber steel-core bullet and added a belt around the cartridge base for proper headspacing (the idea of adding a belt on the base of a magnum cartridge was a British invention by Holland & Holland in 1910 for their larger hunting rifles firing the powerful .375 H&H magnum cartridges). This new cartridge weighed 946 grains (64 gm.) and had a velocity of 2495 feet/sec, delivering 17726 ft-lbf (24033 joules) of energy. By comparison, the .30-06 cartridge (all variants) delivers somewhere between 2800 to 3000 ft-lbf of energy. The job of manufacturing the new .55 caliber cartridge was given to Kynoch Ltd., a well known manufacturer of cartridges in England.

With the cartridge designed, the next goal was to design a rifle around this cartridge. It was simply a bolt-action design with a 5-round magazine, weighed about 35 lbs. (16 kg.) and was about 5 feet 2 inches (1.575 meters) long. The magazine was top-mounted and therefore, the sights were offset to the left to accommodate this. Tragically, the designer of this rifle, Captain Boys, died a few weeks before the rifle went into production in November 1937. Hence, the rifle was renamed as the Boys Anti-tank Rifle in his honor.

The Boys Anti-tank Rifle Mark I. Click on image to enlarge. Public Domain Image.

The rifle was manufactured in three variants. The Mark I variant (as shown in the image above) was the original design manufactured by the Royal Small Arms Factory in Enfield. Notice the round muzzle brake and the T-shaped bipod The Mark I* was given to the Canadian company, John Inglis & Co.  to manufacture and this variant had a V-shaped bipod and flat muzzle brake. The Mark II Airborne variant was designed to be carried by paratroopers and had a shorter muzzle.

When the Boys rifle was delivered, it was not effective against German panzers since the very beginning of World War II. While the bullet fired by this rifle could penetrate through mild steel plate of 23.2 mm. thickness (almost 1 inch thick) at about 90 meters (100 yards) range, the frontal armor of the German tanks was thicker and harder than this and therefore the rifle didn't fare very well against them. However, they proved to be more effective against armored cars and Soviet and Japanese light tanks. The Finns used them against Soviet tanks in 1940. The original steel-cored bullet was later replaced by a tungsten-core bullet (the .55 Mark II cartridge) in an attempt to improve its effectiveness. Despite the cushioned butt pad on the stock, the recoil from this weapon was terrific and often ended up bruising the operator's shoulder, which made soldiers very reluctant to fire it unless it was mounted to a support. This weapon did find some success with the British commandos of World War II (the Desert Rats), who mounted it to the top of their trucks and Bren carriers, when they went on raids in the desert.

Since the rifle had such a heavy recoil, an adapter kit was designed to be used by this rifle for training purposes.

What the adapter kit did was allow the user to mount a smaller .22 caliber rifle to the side of the Boys rifle and fire that via the trigger of the Boys rifle. This allowed for users to learn basic sighting techniques, without having them to bear the force of firing the Boys rifle during training sessions.

The Walt Disney Company was also commissioned to produce a training video for this gun during World War II:

Yes, that is a Disney cartoon animation at the beginning of the first video.

While the Boys rifle was largely ineffective in its original role of stopping German tanks, it was more effective against lighter skinned vehicles, early Soviet and Japanese tanks and armored vehicles. US Marines used it against Japanese bunkers as well. By the end of World War II, this rifle was seen as obsolete and was replaced by bazooka type anti-tank weapons. However, they were still used in the Korean war and in the Philippines until 1960 or so. One was even used in the 1960s by the IRA to disable a British Navy Patrol Boat HMS Brave Borderer by shooting out one of its turbine engines through the hull of the boat.

The Mauser Anti-tank Rifle

In today's post, we will study a special firearm that was developed during World War I. It was the world's first anti-tank rifle and it was developed by Mauser. This particular rifle was called the Mauser Tankgewehr M1918 (or Mauser T-Gewehr for short). The word Tankgewehr is German and means "tank rifle".

During World War I, the invention of the tank revolutionized modern warfare and gave British and French troops a significant advantage on the battlefield. When it was first introduced, the British Mark I tank was almost invulnerable to the ordinary rifles possessed by the German troops in the trenches. The Germans tried several tactics to neutralize British tanks.

The first attempt that the Germans made was to develop a "reversed bullet". This was simply a cartridge with the same case and bullet as the normal cartridge, but the bullet was turned backwards and extra propellant was added to the cartridge case. Since it used the same bullet and cartridge case, it could be fired by the infantry rifles that the Germans were already using. When such a cartridge was fired, the extra propellant would push the bullet at a faster speed than a normal cartridge and because the bullet was placed in backwards, the blunt end of the bullet would hit the tank first. If fired at closer ranges, the bullet would not shatter on the armor plating of the tank, but would instead penetrate it. In many cases, it would not always penetrate, but would significantly dent the tank's armor and cause shrapnel to fly in the interior compartment and kill or wound the people inside the tank. However, this cartridge was only effective at close range and because it carried extra propellant, it could damage older rifles or cause them to burst, thereby endangering its user and people around him.

The next attempt was to develop a special "K-bullet". This bullet was a 7.92x57 mm. bullet similar to what the Germans were already using at that time, but it was made with a hard tool-steel core. This meant that it could penetrate armor better than other bullet types. In fact, it had a 33% chance of penetrating 12-13 mm. thick armor plate at a range of 100 meters (330 feet). Like the reversed bullet, this could also be fired out a standard German infantry rifle. However, the K-bullet was more expensive to produce and hence was only issued to specialized snipers. Also, like the reversed bullet, the K-bullet cartridges also often damaged rifles, especially older ones and therefore wasn't very popular. In addition to this, when the British introduced the Mark IV tank during the battle of Messines Ridge, the K-bullet couldn't penetrate its thicker armor effectively.

Therefore, the Mauser factory came up with an entirely new rifle, specifically designed to fight against armored vehicles.

The Mauser T-Gewehr M1918. Click on the image to enlarge.

Image licensed under the Creative Commons Attribute-Share Alike 2.0 France license by user Rama at wikipedia.org

The Mauser Tankgewehr M1918 was developed in 1918, as the name suggests. It was a bolt-action design, using the same tried and tested Mauser M-98 action that was used in their bolt action rifles from 1898 onwards. The rifle was single-shot and rounds were loaded manually into the chamber. Sights were calibrated between 100 and 500 meters. The rifle and bipod together weighed about 18.5 kg. (or about 40 lbs.), so a two man crew was required to operate this -- a gunner and an ammunition carrier, who was also trained to fire the rifle, in case the gunner was injured.

The cartridge for this rifle was a 13.2x92 mm. cartridge, with a special hardened steel core bullet. The rifle did not have a muzzle brake and there was no recoil pad in the stock either. This meant that the rifle had a very heavy recoil and often injured the shoulder of the person firing it. Nevertheless, approximately 15,800 of these rifles were produced. Unfortunately for the Germans, this rifle came rather late in the war. Mass production of this rifle began in May 1918 and by November 1918, the end of World War I was declared.

This was the world's first anti-tank rifle and pioneered the use of other large caliber firearms in the future. We will study some of those in the following posts.

The Richardson R5 Philippine Guerilla Gun

In our last post, we studied about a survival rifle that was designed for backpackers and hikers. Today, we will study an unusual firearm that was originally constructed in the jungles of the Philippines. We're talking about the Richardson R5 Philippine Guerilla Gun.

First, we will talk about an extraordinary gentleman named Iliff David Richardson, who was responsible for manufacturing and marketing this gun in the United States. Mr. Richardson originally enlisted in the US Navy as an ensign at the start of World War II and was stationed in the Philippines. His PT boat was one of the boats that was involved in the operation to evacuate General Douglas MacArthur out of the Philippines to Australia. He continued to serve on his PT boat until it was sunk by Japanese Navy float planes a month later. After this, he enlisted in the US Army and was involved in the fighting around Cebu city in the Philippines. He and a dozen other Americans attempted to escape in a native outrigger canoe to Australia, but the canoe sank in a storm and Mr. Richardson managed to reach the island of Mindanao after a long swim. There, he came into contact with Philippine resistance fighters and joined forces with them. Since he was a trained ham radio operator before the war, he was put in charge of setting up communications between the various resistance groups and allied forces in Australia and coordinating their efforts. He did this for about 3 years, until the US forces reoccupied the Philippines in late 1944. For his work in the war, General Douglas MacArthur made him a US Army Intelligence major and he had the unusual distinction of holding commissions in both the US Army and the US Navy simultaneously. His heroics came to the attention of the public towards the end of the war and Hollywood even made a movie, "American Guerilla in the Philippines", partly based on his adventures.

Iliff David Richardson in late 1944. Click on image to enlarge.

During his time with the Philippine guerillas, he noticed that they made simple firearms called Paliuntod and Paltik. These were one-shot weapons that were designed to be used to overcome an enemy soldier in a surprise attack and then take his weapon. In this, they were similar in purpose to the FP-45 Liberator pistol that we studied a couple of years ago.

A Paliuntod shotgun. Click on image to enlarge.

These weapons were originally invented and used by Filipino guerillas during the American occupation of the Philippines and continued to be used during World War II and can still be found in use currently. The shotgun above consists of a crude barrel made from a soft metal tube sliding over another tube. The user would push it forward (as shown in the image above) and load a cartridge into the back of it. The firing mechanism was extremely primitive as well. It consisted of a fixed firing pin, which was a nail that was fixed to the handle. To fire it, the user would simply slide the barrel back hard enough so that it slammed against the nail, which would detonate the cartridge and fire it. There was no rifling in the barrel and the weapon was only effective at short ranges and was mainly used to disable an enemy and take his firearm. Several guerillas who had fought with Richardson used these weapons against the Japanese.

After the war, Mr. Richardson came back to the US and found that he was regarded as a celebrity. He started a company called Richardson Industries in 1946 to manufacture the type of weapons that they used against the Japanese. He called his creation the Model R5 Philippine Guerilla gun. Compared to the guns used by the guerillas, the model R5 was made of comparatively better materials.

A basic model R5 Richardson Guerilla gun

It consists of a simple wooden stock with a guide tube attached to it. At the back of the guide tube is a fixed firing pin. The barrel is a smaller diameter steel tube with no rifling, that can slide within the guide tube. The barrel is large enough to hold a 12-gauge shotgun shell. To load this firearm, the user slides the barrel out and inserts a shell into it. Then the user slides the barrel carefully back into the guide tube. To fire the gun, the user grabs the stock with one hand and the barrel with the other hand and strongly slides the barrel backwards to slam the cartridge against the fixed firing pin, which fires the gun. Note that the only thing that holds the breech closed is the strength of the user's two arms. There are no sights on this firearm and it is only meant to be used at close ranges. The little metal piece you see where the trigger should be is actually a safety device. It is simply a metal bolt that prevents the barrel from moving backwards far enough to strike the firing pin. A more advanced model of this rifle has a lever that looks like a trigger, but the mechanism actually controls a cam that prevents the barrel from sliding forwards or backwards until the trigger is pulled. The advanced model also has a grip attached to the barrel to make slamming the barrel back easier. The basic model has only 5 parts and the advanced model has 17 parts! The stock has the name of the manufacturer ("Richardson Industries Inc., East Haven, Conn., USA"), carved on one side and the words "Philippine Guerilla Gun, Patent Pending" carved on the other side (this message is visible in the image above). The stock is made of cheap wood and there is no butt plate.

Barry from Moss Pawn and Gun demonstrating the advanced Richardson model. Courtesy Iraqveteran8888's channel.

Despite the fame of the creator, this gun never sold very well because it was very impractical to use and production stopped about one year later. The price of this gun, when it was first sold, was only $7, but it now sells as a collector's item for as much as $350-$400 today.

The AR-7 Survival Rifle

A few months ago, we had discussed the amazing Soviet Space Pistol (TP-82), which was designed to be used as a survival weapon in remote areas. In today's post, we will look at a weapon that was designed in the US for a similar purpose. We are talking about the Armalite AR-7, known these days as the Henry Survival Rifle.

The Armalite AR-7 was designed in 1958 by Eugene Stoner, the same gentleman who designed the AR-15 and M-16 rifles. The AR-7 was based on the older AR-5 which was developed as a survival weapon designed to be used by aircraft personnel and carried in emergency kits stored aboard aircraft. The AR-5 was adopted by the US air force, but they only ordered very small numbers, therefore Armalite used some of the tooling that was originally developed for the AR-5 to create the AR-7 for the civilian market. The rifle was released to the civilian market in 1959. It was meant to be used by bush pilots, backpackers, hikers and amateur explorers.

As a bare-bones survival rifle, one of the primary requirements was for the design to be light and portable. Therefore, the AR-7 was made from plastics and aluminium alloys to reduce weight. The rifle was also designed to be compact so that it could fit inside a backpack. Therefore it was designed so that the parts could be disassembled and stored inside the plastic stock!

An AR-7 stored in a disassembled state. Click on image to enlarge.

When the rifle is stowed within its stock, the whole package can float on water! This rifle is designed to use the popular .22 LR cartridge, which is the most commonly available rifle cartridge in the world. It has a semi-automatic action and can hold 8 cartridges within its magazine. The entire rifle weighs 3.5 pounds (about 1.58 kg.) The rifle is also designed to be disassembled without any tools. The stock attaches to the receiver with a long screw bolt and the barrel screws on to the receiver, both of which can be manipulated using just a person's hands.The entire rifle can be assembled or disassembled in about 30 seconds. 

An assembled AR-7 rifle. Click on image to enlarge.

The rifle was designed for an 8 round magazine originally, but there are now other magazines for it that can hold 10, 15, 25 or 50 rounds as well. Accuracy is pretty decent and it can be used to hunt small game animals.

Armalite sold the rights to the design to Charter Arms in 1973. According to some people, Charter Arms didn't manufacture their rifles with the same quality as Armalite and the rifle started to gain a bad reputation during this period. Charter Arms later sold the design to the Henry Repeating Arms company in 1980. The Henry Repeating Arms company slightly revised the design and produced a much better quality version than Charter Arms and after that, the bad reputation it had collected in the previous few years went away.

The version that is now made by Henry Arms has two 8-round magazines stored in the stock (latest versions have 3 magazines). The plastic stock is now made of ABS plastic which is tougher than the original plastic stock and does not crack easily. It is also much more water-resistant than the older stock. The receiver and barrel are coated with teflon for better corrosion resistance

An AR-7 was even featured in the James Bond movie To Russia With Love starring Sean Connery.