Sunday, November 22, 2015

Early Cartridge Technologies: Linen Cartridges

A few weeks ago, we began to study an early form of cartridge: the paper cartridge. Where we left off, paper cartridges had advanced to the point where the paper was treated with chemicals to make it more combustible.

The main problems with paper cartridges are that they aren't very water resistant and the paper is somewhat fragile. As the bullet could be rather heavy, the weight of the bullet could cause the paper to tear as well. There was a need for a cartridge to be made of a more durable material and that's when the linen cartridge was born.

A .52 caliber linen cartridge for a Sharps rifle. Click on the image to enlarge.

In 1852, American inventor Christian Sharps invented a linen cartridge, to go with his Sharps rifle (which was earlier invented in 1848). The linen cartridge was a great improvement over the paper cartridge because it could withstand rough handling better, without breaking open. A linen cartridge also held its shape better than a paper cartridge could. The back of the linen cartridge had a piece of nitrated flash paper (which we studied in the last post) to provide the ignition. The linen used to make the cartridge body was treated with starch to make it stiffer. Linen cartridges were also treated with chemicals to make the linen more combustible, similar to that of paper cartridges that we studied earlier. Like the paper cartridges, the bullet was glued on top with sodium silicate glue.

For a while, cartridges were made for the Sharps rifle with both paper and linen, but the linen cartridge gradually started to find some backers. In the words of a Major W.A. Thornton:

"The making of Sharps Cartridges with paper must be abandoned and linen must be used in the formation of the cylinder. More care cannot be given in the making of cartridges than is bestowed in our laboratory. The fact is that the ball is too heavy for the paper, and worse than that -- the paper is sometimes softened by the lubric which causes it to break by the weight of the ball. From this date, I will make no more of paper, but I will make the powder cylinder of linen."

What the Major is describing are two flaws of the paper cartridges used by the Sharps rifles. The first is that the weight of the bullet is so great that a paper cartridge cannot hold its shape and often tears open by itself, due to the weight of the bullet. The second problem is that the lubricant (spelled in his letter as "lubric") also softens the paper and weakens it, thereby causing the paper to break. Since the lubricant is necessary to reduce the fouling inside the barrel, a stronger material must be used for the case body and this is why linen was used.

Linen cartridges were used by both the Sharps rifle and the Starr carbine during the Civil War.

In our next post, we will study another durable material that was also used to make cartridges during that period of time.

Monday, November 16, 2015

The Pencil Test

Imagine you're looking at a used pistol with an intent to purchase it. If it has been well used, chances are that some parts may be worn out or broken. One part, in particular, is the firing pin, which may be broken, bent, blunted etc. Another part of interest is the mainspring, which may have lost some of its strength. Or perhaps you stripped your pistol in order to clean it, and you aren't sure if you put it back together properly. There is a simple test to verify that the firing pin and mainspring are working satisfactorily and this test is the pencil test, which we will study about today. The only tool you'll need to conduct this test is a pencil with an eraser tip on one end:

A standard #2 size pencil. Click on the image to enlarge. Public domain image.

  1. First, make sure the pistol is empty.
  2. Cock the pistol, making sure that it is still empty.
  3. Insert a pencil with the eraser end first into the barrel and push it as far as it will go (do not force it, just push it in gently). For best results, use a new wooden pencil (such as a standard #2 size pencil, like the one pictured above), with the eraser in good condition
  4. Hold the pistol vertically, with the barrel end aimed upwards.
  5. Make sure that the pistol is indeed empty, then pull the trigger.
  6. If the firing pin and mainspring are working correctly, the pencil will move noticeably. In many pistols models, the pencil will actually come shooting out of the barrel. If the pencil doesn't move, or only moves weakly, there may be a problem with the firing pin or mainspring.
This test works on various pistol models, both hammer-fired and striker-fired types. Of course, the distance that it comes shooting out of the barrel depends on the model of pistol and also the wear and tear of the parts. For 1911 pistols in good condition, the pencil should come flying out and go at least a few feet up in the air. Glock pistols will also propel the pencil out a good amount of distance, but generally not as far as a 1911. Of course, the test also depends on the shape of the firing pin and the hardness of the eraser. For instance, in some models of M&P pistols, the firing pin may pierce the eraser instead of shooting it up. In such cases, if the pencil is put in with the unsharpened end in first, it may come flying out better. Alternatively, a plastic ballpoint pen, such as a Bic, may be used. In general, hammer fired pistols tend to propel the pencil out farther than striker fired models.

For pistols that are equipped with decocking levers (such as Sig Sauer, Ruger P95, Beretta M9 etc.), a similar test may be used to ensure that the decocking safety mechanism is working properly. As before, the pistol is cocked and the pencil is pushed in as before and the pistol is held vertically. Then, instead of pulling the trigger, the decocking lever is pushed instead. If the decocker is working correctly, the pencil should not move at all. If it moves, that means the decocker is not working properly and the firing pin is contacting the eraser.

Now on to some videos, so that you can see what it looks like.

The first video is from user Sadie Thorne on youtube and shows a quick test with a 1911 type pistol.

This video comes with no explanation, but shows the test very nicely. Notice how far the pencil comes flying out of the barrel, when the trigger is pulled.

The next video is by stdlfr11 and shows the same test done using a CZ-75 pistol.

This video has the user giving an explanation of the test, as it is being done. Note that while the pencil moves noticeably, it doesn't move as far as the one in the previous video. The reason for this becomes clear when the user pulls the pencil out as you can clearly see the indentation that the firing pin made on the eraser, which could explain why it didn't fly out as much. If the eraser had been harder or if the user had put the pencil in with the unsharpened end first, it would probably have flown out of the barrel much better. The test does show that the firing pin is functional and is not broken.

So there you have it, a simple test using a pencil ensures that the firing pin and mainspring are working satisfactorily.

Saturday, November 14, 2015

Early Cartridge Technologies: Paper Cartridges - III

In our last post, we saw the advances in paper cartridge technology to handle expanding bullets. In today's post, we will study more advances in paper cartridge technology around the time that percussion caps and revolvers started becoming popular.

Early Colt Paterson revolvers. Click on the image to enlarge. Public domain image.

With the advent of percussion cap revolvers, such as the Colt Paterson models pictured above, most people loaded their revolvers from paper cartridges exclusively. The paper cartridges were therefore modified a bit to take advantage of these new developments in firearms.

In the picture above, note that the two Colt Paterson 1839 model revolvers have a loading lever under the barrel, whereas the 1836 model doesn't have this feature. We will see how that is used with the cartridges that we will study today.

Paper cartridges for a .36 caliber Colt revolver.; Click on the image to enlarge

As you can see in the images above, the bullet is now in the front of the cartridge (unlike the designs we studied in our last post). The bullet is attached to the cartridge with glue. Also, the shape of the cartridge has changed a bit, so that the paper part now forms a conical shape instead of a cylindrical shape. This was a deliberate design choice, so that it is easier for the user to insert the cartridge into the front of the cylinder. Unlike previous designs, there is no need to tear the paper and pour the powder into the chamber. Instead, the loading lever is used to ram the entire cartridge into the chamber. Because of the shape of the cartridge, the cartridge paper automatically tears open when it is compressed into the chamber. Some cartridges were equipped with a protective outer layer around the cartridge, to keep it safe from moisture, and these would have a tiny tear tab to remove the outer layer before loading the cartridge.

A glue made of sodium silicate was used by the Colt Manufacturing Company to hold the bullet to the cartridge, as well as seal the paper part. This was what was used by Colt between 1851 to 1873, until they started to produce brass cartridges in 1873. Sodium silicate has the advantages of resisting high temperatures, as well as being cheap and easily available. Sodium silicate was also used to cement the top wad of shotgun shells and was heavily used by American farmers who reloaded their own shells in the 1870s, as sodium silicate was the same material used to preserve eggs as well.

One more innovation made to these cartridges was to the paper material as well. In order to make the ignition of the powder more reliable, the paper was treated with chemicals to make it burn better. This paper is called nitrated paper, as it is manufactured by soaking it in a solution of potassium nitrate and then drying it. This treatment makes the paper much more flammable than ordinary paper. Such cartridges are called combustible cartridges, because the paper burns almost completely upon ignition. A properly nitrated paper leaves behind less ash and residue, thereby making it easier to clean and reload the weapon.

Another formula for making combustible paper used a solution of nitric and sulfuric acids and was used by both Colt Manufacturing and Dow Chemicals, as well as some other manufacturers in the 1800s. These are essentially the same chemicals used to produce guncotton, which we had studied a few years before. Paper that is treated this way is called flash paper. This paper also burns quickly and leaves very little ash behind, but it is much more unstable than nitrated paper, and in the early days, it was also prone to spontaneous combustion. This is why flash paper did not gain much popularity in the firearms industry. These days, the only people using flash paper are magicians, who use it to produce spectacular flames when performing magic tricks.

With the advent of metallic cartridge technologies, the use of paper cartridges started to reduce. However, there are still some applications for which paper is used. For instance, until about 1960 or so, many shotgun shells were made of paper bodies, with a brass base and rim. The reason for this was because it was cheaper and easier to make the body out of paper than to make the entire shotgun shell out of brass. Around 1960, shotgun shells started to use plastic bodies instead of paper, and a majority of modern shotshells today make use of plastic. Nevertheless, it is still possible to buy paper shotshells even today.

The bodies of these cartridges are made of a cardboard paper and are coated with wax to provide some resistance to moisture. They aren't as common as they were back before 1960, but there are still some manufacturers making them.

Saturday, November 7, 2015

Early Cartridge Technologies: Paper Cartridges - II

In our last post, we looked at the earliest forms of paper cartridges. In today's post, we will look at more developments in that field.

As firearms technologies improved, smoothbore muskets began to be replaced by rifled barrels for greater accuracy. The invention of expanding bullets, such as the Minie bullet, made it possible for firearms to not only shoot accurately, but also improved the gas seal without the need for thicker wadding, because the bullet would expand and produce the gas seal itself. The main problems to solve here were to reduce the amount of fouling produced by the black powder and lead from the bullet, as well as to keep the cartridges from being affected by bad weather. The solution to both these issues was to provide a coating to the paper cartridge case, in the form of a mixture of beeswax and tallow. This coating allowed the cartridge to be somewhat water resistant, as well as provided lubrication to the bullet.

The lubricant made it easier to push the bullet down the barrel of the muzzle loader and also softened the residue inside the barrel, so that most of it could be pushed out of the way easily when reloading. This helped reduce the problem of powder fouling in the barrel, though it did not solve it.

Since the bullet expanded and provided the tight seal on firing, the paper needed to be thinner than previous paper cartridges, so it could fit between the bullet and the barrel properly. However, the thin paper could cause the body of the cartridge to not be sturdy enough. To get around this problem, cartridges were often made using multiple layers of paper, some thick and others thin. The following instructions and illustrations are taken from an instruction manual dating back to 1853 for the Enfield rifle. The manual explains that soldiers might find themselves in the position of having to make their own cartridges in the field, and therefore the manual shows how this was done.

Three separate papers used to manufacture an Enfield cartridge. Public domain image. 

Tools used to manufacture the Enfield cartridge. Public domain image.

The first image shows the different paper shapes used to make a single cartridge, along with their sizes. The paper shape on the right (labelled as "stiff paper") is made of a thicker paper material and forms the body of the cartridge and gives it the strength, so that the cartridge does not deform easily. The paper shape in the middle (labelled "inner envelope") is made of a thinner paper material. It wraps in a thin tube around the thicker paper and then blocks it on one end, thereby separating the powder from the bullet. The third piece of paper on the left (the "outer pattern") is also made of a thinner paper material. It wraps around the bullet and the other two tubes, thereby enclosing the bullet and powder in one packet.

To manufacture one of these cartridges, the instructions are as follows:
  1. Make the powder case: This is done by rolling the "stiff paper" pattern tightly around the mandrel around 2.5 times. The mandrel is laid opposite to the side AB, with the base of the mandrel head coinciding with AD. After the "stiff paper" is rolled around the mandrel, the "inner envelope" paper is placed on top of it and rolled around it. The second paper overlaps the first one, so the excess is pushed into the hollow at the base of the mandrel, making use of the point to adapt the paper to the cavity which is to receive the point of the bullet, being careful to secure the bottom of the powder case, so that no powder can escape from it.
  2. Attach the bullet to the powder case: Put the point of the bullet well into the cavity of the powder case. Then roll the "outer envelope" paper tightly around the bullet and powder case, with the mandrel still in it. Then twist or fold the overlapped paper as close as possible to the base of the bullet. Then place the base of the cartridge on the table and withdraw the mandrel carefully from the other end, by pressing the powder case with one hand, while pulling the mandrel with the other, the aim being to not separate the powder case from the bullet. The powder case must be kept as close to the bullet as possible, otherwise the cartridge will not be usable.
  3. Charge the cartridge case: Place a funnel at the mouth of the cartridge case and pour in about 2.5 drams of black powder, or a lesser quantity, according to the firearm used. Remove the funnel, being careful that none of the powder escapes between the inner and outer envelopes and then secure the charge by squeezing the tops of the two envelopes close to the top of the stiff paper of the powder case, and then giving them a slight twist with inward pressure, laying the ends on the side of the cartridge. Three slits are made in the outer envelope to facilitate its detachment when fired.
The next picture is in color and shows how these three papers combine together in a complete cartridge:

Internals of an Enfield cartridge from the 1850s. Click on the image to enlarge.
Public domain image courtesy of user Zerodamage at Wikipedia/
  1. Lubricate the cartridge: In this step, the base of the cartridge case is dipped up to the shoulder of the bullet, into a lubricating mixture composed of 5 parts of beeswax and 1 part of tallow.
A complete Enfield paper cartridge. Public domain image.

Cartridges were then packed in bundles of ten, and each packet was labelled as shown below.

The second line indicates that these cartridges are for the Enfield model 1853 rifle musket. The next line indicates that the bullet is of .55 inches in diameter. The word "wax" is to indicate the composition of the lubricant and the three horizontal lines after that indicate that the outer paper layer has the three cuts (as detailed in step 3). The next line indicates how much black powder is in each cartridge (2.5 drams) and the last line indicates that each bullet has a plug made of wood in its base and this plug enables the bullet to expand when the cartridge is fired.

The packets were then tied together with strong twine and packed into barrels, by placing the packets around the sides of the barrel, with a cylinder of percussion caps being placed in the center, with the ratio of 75 percussion caps for every 60 cartridges in the barrel.

To load such a cartridge into a rifle, the powder end of the cartridge is opened by tearing the thin outer paper envelope and the powder is then poured into the muzzle of the rifle. Then the bullet end is inserted into the muzzle, up to the level of the thick paper tube, which is then torn off and discarded. The bullet and the remains of the thin outer envelope are then pushed into the barrel using the ramrod and the rifle is then cocked and prepared for firing.

Interestingly, the use of lubricated paper cartridges was one of the causes of the Great Indian Mutiny of 1857. The sepoy soldiers of British India were required to bite on the cartridges to open them, as part of the loading procedure. A rumor spread that the cartridges were greased with beef fat (offensive to Hindus, who are forbidden to eat beef) and pig fat (offensive to Muslims, forbidden to eat pork). There were already rumors that the British authorities were trying to destroy the religions of the Indian people and the rumors of the content of the cartridge grease convinced sepoys of the Bengal regiment that their fears were justified. This was cited as one of the causes for the mutiny to start.

In our next article, we will look at further improvements to the paper cartridge, as we enter into the era of revolvers.

Wednesday, November 4, 2015

Early Cartridge Technologies: Paper Cartridges - I

Since we were discussing cartridge rim types in our recent series of posts, your humble editor decided to go back in time to the first cartridges. We had already discussed paper cartridges some time back when this blog first started, but it might be nice to revisit that topic in detail.

A paper cartridge is simply a cylinder or conical shaped object made of paper and filled with a bullet, some black powder and sometimes, a lubricating substance (such as wax or lard). The paper was often of a thicker type. In later years, a special type of paper, called cartridge paper, was specially developed for this purpose. From a firearms perspective, one of the biggest advantages of paper cartridges was that it allowed the users to reload their firearms quicker than before.

According to W.W. Greener's book, The Gun and its Development, the use of paper cartridges has been going on for a while. It was stated that the soldiers of Christian I, Elector of Saxony (currently in modern Germany), were using paper cartridges in 1586. Interestingly, Christian I of Saxony was from the House of Wettin, some of whose descendants are the Royal family of the UK. Greener also states that in the Dresden museum, there are Patronenstocke and other evidence to show that cartridges were in use, as early as 1591 (since the book was written in the early 1900s and Dresden was bombed heavily in World War II, your humble editor is not certain if the specimens still exist there). Finally, an author named Capo Bianco wrote in 1597, that cartridges had long been in use among Neapolitan soldiers. In England, the British Patent office has a record from 1777, when one William Rawle patented several "instruments for carrying soldiers' cartridges". Therefore, we can see that paper cartridges have been in use for quite a while.

A typical paper cartridge. Public domain image.

As we studied a long time ago, most of the early firearms were muzzle-loading, with no rifling at all. Early cartridges for such weapons simply consisted of a paper tube with three pieces of thread: two threads tied on each end to seal the packet and a third thread somewhere in the middle to divide the paper tube into two compartments, such as the one in the image above.

The first compartment (the smaller one) contained the bullet (or bullets), which were spherical shaped because the muskets didn't have rifling. The second compartment (the larger compartment) contained a pre-measured quantity of black powder.

To load the musket, the user would use the following process:

  1. Hold the musket level and open the cover of the flash pan.
  2. Bite open the cartridge on the side containing the powder and pour a small quantity of the powder into the flash pan to prime it. Then close the cover of the flash pan.
  3. Turn the musket up vertically and pour the remaining powder into the barrel.
  4. Crumple up the paper and insert the ball and paper into the muzzle of the musket.
  5. Use the ramrod to push the ball and paper down the barrel of the musket.
  6. Prepare the musket for firing by cocking the flintlock mechanism.
Since the quantity of black powder in the cartridge is already measured in advance, this eliminates the  need for the user to measure the proper amount of powder during reloading. Also, since the bullet ball is already wrapped in the packet, the user doesn't need to search around in a separate bag to find a ball for reloading. As smoothbore muskets of the era were loaded with lead balls that were smaller than the diameter of the barrel, the cartridge paper also served as a patch to provide a good gas seal in the barrel.

Paper cartridges of this early type were generally designed with thicker paper, so that they could withstand rough handling.

It must be mentioned that black powder leaves a lot of residue in the barrel, therefore it becomes harder to push the ball in after every shot, until the barrel is properly cleaned. Also, black powder does not like damp conditions very much.

In the next part, we will look at some developments in paper cartridge technology that solved some of these problems, as well as handling newer firearm technologies, such as rifling.

Saturday, October 31, 2015

Cartridges Rims: Rimmed vs. Semi-Rimmed vs. Rimless vs. Belted vs. Rebated - Part III

In our last couple of posts, we looked at a few cartridge rim types: the rimmed cartridge, semi-rimmed and rimless types. We will look at a couple more rim types in today's post: the belted type and the rebated rim type.

As we noted in our previous post, the basic problem with rimmed cartridges was reliable feeding from box magazines, as the cartridge rims would interfere with each other in this type of magazine. One way to solve this was to reduce the diameter of the rim, as we saw with the semi-rimmed type of cartridge. Of course, the smaller rim made it trickier to headspace the cartridge in the chamber properly. Around the same time, another type of cartridge was introduced in 1905 to solve both issues: the belted cartridge.

The belted cartridge design originated in England and was designed by the famous sporting gun manufacturer, Holland & Holland. A belted cartridge is similar to a rimless cartridge in that the rim is around the same diameter as the cartridge case and there is an extractor groove in front of the rim for the extractor claw to fit in and pull out a spent cartridge. The belted cartridge differs in that in front of the extractor groove, there is a raised ring in front of the extractor groove.

The belt acts similar to the rim for the purpose of headspacing the cartridge in the chamber properly. This design allows smooth feeding through box magazines, but also has the advantage of providing positive headspacing, just like a rimmed design. Most belted type cartridges are designed for high-powered hunting rifles.

Headspacing on a belted cartridge. Click on the image to enlarge. Public domain image.

The origin of this type of cartridge had to do with when black powder was being replaced by smokeless powders, specifically cordite. As we saw in the linked article about cordite previously, cordite is composed of long strings of a light brown color, which are packed into a cartridge case in bundles like spaghetti. The prevailing production method of these cartridges in England consisted of inserting small bundles of cordite into a straight-walled case, which was then necked down to the final shape and the bullet was seated. Because of the long strings of cordite, cartridge cases using this propellant tend to have long sloping shoulders.

A .375 Holland & Holland magnum belted cartridge

When these cordite cartridges were first developed, most rifles were still single shot designs, so they were designed as rimmed cartridges. However, as the bolt-action rifles started to become popular, there began a demand for proper feeding from box magazines and hence, the belted cartridge was developed. The first belted cartridge was the .400/375 Holland & Holland Belted Nitro Express cartridge, and it was specifically developed to compete against the German 9.5x57mm Mannlicher-Schonauer cartridge, which was being adopted by Holland & Holland competitor in England, Westley Richards. However, soon after, a German gunmaker named Otto Bock designed the 9.3x62 mm Mauser cartridge. This cartridge was made to be fired out of the Mauser M1898 rifle, which was designed to be mass-produced and cheaper than most British rifles at that time. The cartridge and rifle rapidly became popular with African hunters, because of its all-round capability to be used against animals ranging from the smallest antelopes to the largest elephants. In response to this, Holland & Holland developed the .375 Magnum Belted cartridge in 1912. The belted design allowed cases to feed and extract reliably in the tropical environments found in India and Africa. The .375 H&H Magnum rapidly became one of the most popular all-round hunting cartridges in the world, and in many regions of the world, it is considered to be the legal minimum caliber allowed to be used to hunt large animals.

Interestingly, in the US, the belted cartridge has become synonymous with the word "magnum" and there are several calibers of belted cartridges available, such as: .257 Weatherby Magnum, .300 Weatherby Magnum, .375 Winchester Magnum, .350 Remington Magnum etc.

Rebated cartridge: In this type of cartridge, the rim of the cartridge has a noticeably smaller diameter than the body of the cartridge case. The rim is only used for extraction purposes, and proper headspacing is achieved by using the cartridge mouth or bottleneck body shape. The rationale behind this type of cartridge is to offer increased case capacity (and therefore, more power), without changing the bolt face of the weapon and thereby, keeping most of the other parts of the weapon unchanged.

For instance, in the 1980s it was desired to increase the power of police pistols which use 9x19mm parabellum cartridge. In response to this, Evan Whildin, a vice-president of Action Arms, designed the .41 Action Express cartridge.

A .41 Action Express cartridge on the left, compared to a 9x19mm Parabellum cartridge on the right.
Click on the image to enlarge. Public domain image.

The image above shows a .41 Action Express (.41 AE) cartridge on the left, compared to a 9x19 mm. Parabellum cartridge on the right. The reader will immediately notice that the cartridge on the left is fatter and longer, but what is interesting to note is that the two cartridges have the same sized rims at the bottom. In the case of the .41 AE, since the case body is fatter, the rim is actually smaller diameter than the case body.

The idea behind the .41 AE was that it allows converting a 9 mm. pistol to use this cartridge, merely by replacing the barrel, mainspring and magazine. Since it has the same sized rim as the 9x19 mm., the other parts of the pistol, such as the extractor claw, bolt, firing mechanism etc., can be reused and therefore, it keeps the total cost of converting the weapon relatively low.

However, when it was introduced, many of the ammunition manufacturers backed the .40 S&W cartridge, which had similar performance, and therefore the .41 AE cartridge didn't become popular. Nevertheless, the idea of using a rebated rim cartridge to interchange with another weapon stayed on. For instance, the .50 Action Express (.50 AE) cartridge is designed to be used with the American/Israeli Desert Eagle pistol. The rim of the .50 AE is the same diameter as the .44 Remington Magnum cartridge, which was the most common caliber cartridge used by the Desert Eagle. By interchanging only the barrel and magazine, a Desert Eagle originally designed for .44 magnum, can be used to fire the .50 AE cartridge.

Other cartridges that use a rebated rim design include Winchester Short Magnum, Remington Ultra Magnum, Winchester Super Short Magnum, Remington Short Action Ultra Magnum, the .50 Beowulf etc. The .50 Beowulf has the same sized rim as the 7.62x39mm cartridge used by AK-47 and AKM rifles and is designed to be used by modified AR-15 rifles.

Happy Halloween everyone and stay safe!

Monday, October 26, 2015

Cartridges Rims: Rimmed vs. Semi-Rimmed vs. Rimless vs. Belted vs. Rebated - Part II

In our last post about various cartridge rim types, we looked at the rimmed cartridge. As we noted in the last post, rimmed cartridges are some of the earliest metallic cartridges developed and they work very well with revolvers and shotguns and rifles with tubular magazines, but not so well with box magazines. There are ways to work around this problem by carefully placing the cartridges in the magazine, as was done by the Lee Enfield and Mosin-Nagant rifles, which we saw in the last post, but these rifles have relatively small sized box magazines with less capacity.

Since box magazines can fit more cartridges in a smaller package than tubular magazines or revolvers, by the end of the 19th century, more and more weapons (especially military weapons) began to feature them and with increasing magazine capacities as well. Therefore, the cartridge rim type needed to be fixed to work well with larger capacity box magazines. There were two different cartridge rim types that were developed to fix this issue:
  1. Semi-rimmed type
  2. Rimless type
Semi-rimmed cartridge: This was one of the first attempts to fix the issue with rimmed cartridges and box magazines. The diameter of the rim is slightly larger than the case diameter, but only marginally so. 

Click on the image to enlarge. Public domain image.

The rim is still used for headspacing the cartridge to the proper depth in the chamber. However, since the diameter of the rim is barely larger than the case, there is less interference with the rim of the next cartridge in the magazine. The rim is wide enough that it is also used by the extractor to pull the cartridge out of the chamber. Examples of semi-rimmed cartridge include the .38 ACP (as illustrated above), the 6.5x50 mm. Arisaka cartridge, the .401 Winchester etc. This type of cartridge is not seen much since the rimless type of cartridge (which we will see below) was developed, but there are still some new cartridges of this type, for instance the .500 S&W Magnum cartridge developed in 2003.

A .500 S&W Magnum cartridge. Click on the image to enlarge.
Image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported by Peter Gnanapragasam

The .500 S&W Magnum rim is used to headspace the cartridge properly in a revolver, but it can also be used in other magazine types because it is a semi-rimmed cartridge.

As manufacturing technologies for cartridges improved, it became possible to manufacture cartridges accurately enough to headspace off the case mouth (for straight cartridge cases) or case shoulder (for bottlenecked cartridge cases). This led to the development of another cartridge type: the rimless type.

Rimless cartridge: Despite the name, rimless cartridges do have a rim. However, in this type of cartridge, the diameter of the rim is almost the same as that of the cartridge case body. There is only one purpose of the rim: it is used by the extractor to pull the cartridge out of the chamber. There is a groove between the rim and the case body, into which the lip of the extractor can engage to pull the cartridge out,

Since the diameter of the rim is the same as that of the case, obviously we cannot use the rim for headspacing the cartridge in the chamber. So how does it work for these cartridges? The following images show us how this is done:

In the case of straight cartridge cases, the case mouth is not crimped onto the bullet, as is done with revolver cartridges. This leaves a little projection in the case mouth that can be used to headspace the cartridge in the chamber correctly:

Click on the image to enlarge. Public domain image.

The above image shows a .45 ACP cartridge loaded into the chamber. Since the cartridge rim is the same diameter as the case body, this cartridge is headspaced against the throat of the cartridge.

Another way to do it is to shape the cartridge into a bottle-neck shape. For this type, the headspacing happens against the shoulder of the cartridge.

Click on the image to enlarge. Public domain image.

As you can see in the image above, the contact point at the shoulder of the cartridge ensures that the cartridge fits into the chamber at the proper depth.

As manufacturing technologies of cartridges improved in the late 1890s, it became possible to mass produce rimless cartridges that would headspace correctly. The rimless cartridge type quickly became the most popular type of cartridge and has remained so to the current day. Since it has no protrusions to complicate the feeding process, the rimless cartridge type has become well suited for most higher capacity modern magazine types, e.g. box magazines, drum magazines, ammunition belts etc. The easier feeding process also made it possible to produce modern rapid-firing weapons, such as machine guns, sub machine guns etc. Some early rimless cartridges include the 9x19 mm. Parabellum pistol cartridge (Luger cartridge), the .30-03 cartridge from 1903, followed by the .30-06 from 1906, the .45 ACP designed by John Browning in 1904 etc. All these cartridges are still widely used currently, along with more modern designs, such as the 7.62x51 mm. NATO / .308 Winchester and 5.56x45 mm. NATO / .223 Remington cartridges.

In our next post, we will study a couple more types of cartridge rims.