What is Keyholing?

When a person fires a rifled weapon towards a paper target, the usual result expected is that a round hole corresponding to the diameter of the bullet will appear on the target. However, sometimes a larger hole appears, often the hole may appear longer in one direction than the other, such as shown in the image below:

An example of keyholing. Click on the image to enlarge.

These larger holes sometimes resemble a keyhole and therefore, the effect is called keyholing. We will study the causes of keyholing in today's post.

By looking at the shapes of some of the holes in the above target, the reader may notice that some of those holes look distinctly like the shape of a bullet going through the target sideways. In fact, this is exactly what has happened.

Under normal working conditions, the rifling of the barrel imparts a spin on the bullet, which stabilizes it in the air and makes it travel with the nose pointed forward always. However, if the bullet is not stabilized properly when it comes out of the barrel, it will wobble in the air or repeatedly tumble over itself while traveling to the target. Thus, when it strikes the target, it may not strike it with the nose precisely pointed forward and will therefore leave a larger hole.

In the above image, we see three holes. Observe that all three holes are somewhat larger than the diameter of the bullet. The top most hole is shaped like an oblong and was caused by a bullet not flying straight when it impacted the target. The middle hole is more round, but still has a pointed hole on one end showing that the bullet was wobbling in the air when it hit the target. The bottom hole clearly shows that the bullet was toppling end over end and hit the target sideways.

So what causes the bullet instability through the air? There are several causes for this:

1. Rifling in the barrel could be worn out, therefore it does not impart enough spin to the bullet while it is leaving the barrel. 
2. The bullet might be undersized and is therefore not engaging the rifling properly.
3. The rifling twist rate may not be adequate for the weight, shape and profile of the bullet. For example, the M855 cartridge and the L110 cartridge are both designed for the M16A2. The bullet from a M855 (or SS109) cartridge can be adequately.stabilized by a barrel with a 1 in 9 twist rate (i.e.) 1 turn every 9 inches (228.6 mm.) of barrel length. On the other hand, the bullet from the L110 tracer round cartridge does not adequately stabilize at this twist rate and needs a twist rate of at least 1 in 7 (i.e. 1 turn every 7 inches (180 mm.)) for the tracer bullet to stabilize. This is because while the bullet diameters are the same, the weight,  distribution of mass throughout the bullet and the bullet profile shapes are different, which causes the instability. Therefore, M16A2 rifles come with a 1 in 7 twist rate barrel, so that they can be used with both bullet types.
4. Leading in the barrel could also cause the bullets to not spin as much when they come out of the barrel.
5. Damage to the barrel near the muzzle may cause the bullets to wobble or tumble as they come out.
6. The bullet does not always immediately stabilize in the air as it leaves the barrel and needs to travel a little distance in the air before it gains stability. If the target is too close, the bullet may be still wobbling in the air a bit, by the time it hits the target.
7. The bullet may have hit something on the way to the target, causing it to tumble in the air for the rest of its journey.

An unstable bullet is undesirable because it flies unpredictably in the air and therefore affects the accuracy of the firearm. An unstable bullet also loses velocity faster and it may not transfer as much energy to the target when it strikes it. 

Keyholing is a sign that the bullets are not being stabilized properly. If a gun shoots maybe one keyhole in 500 shots, it may just be due to a bad bullet, but if it regularly shoots keyholes, then that means there is a problem with the barrel or bullets or both, which needs to be fixed.

Ancient Techniques of Rifling Machines - IX

In our last post in this series, we studied a completely assembled rifling machine, as used by ancient gunsmiths. Until now, what we were studying were a bunch of descriptions and some hand-drawn pictures (hopefully not too badly drawn :)). It is now time for show and tell. In today's post, we will look at some actual images and movies of people using machines to cut rifling by hand.

Some of the following images are taken from a book published in 1941, called Rifle Making in the Great Smoky Mountains, authored by Arthur I. Kendall for the US National Park Service. This book is now in the public domain.

First up, we have a picture of a person using a spring pole lathe to make a wooden cylinder, as the first part of constructing an indexing guide:

Click on the image to enlarge. Public domain image.

Notice how the woman is powering the lathe with her foot, while using her hands to shape the log into a cylinder. For those who like to see one in action, here's a short movie demonstrating a spring pole lathe being used by a person:

After the log is shaped into an uniform cylinder, the next step to making an indexing guide is to mark the spirals on the outside of the log surface.

Marking the indexing guide. Click on the image to enlarge. Public domain image.

In the above image, the woman has wrapped a thin ribbon around the cylinder's outer surface and is marking the edges of the ribbon with a pencil. She will then use a chisel to carve out the wood between the pencil marks.

Cutting the indexing guide. Click on the image to enlarge. Public domain image.

In the above image, the woman is carving out the indexing guide using a sharp chisel. Typically, the depth of each groove is about 1/2 inch. Notice that she's cutting multiple grooves on this guide. The description we studied earlier only relied on a single groove, but multiple grooves can be used for more accuracy.

Part of the rifling machine with indexing head, head piece and tail piece assembled. Click on image to enlarge. Public domain image.

The above image shows a partially assembled rifling machine. The indexing head, head piece and tail piece have been assembled and attached, similar to what we had studied earlier here.

A complete manual rifling machine. Click on the images to enlarge. Public domain images.

In the above two images, we see the rifling machine completely assembled, similar to the one we had studied earlier here.

After seeing all the pictures, let us now watch some movies showing this machine in action.

In the above movie, the gentleman describes how he made his indexing guide, using a process very similar to what we studied earlier. Also notice that unlike the pictures above, his indexing guide only has one groove on it. The gentleman also goes on to describe the process of cutting the grooves in some detail.

In the above movie, we see a gunsmith from the Hensley settlement in Ewing, VA, showing us how his rifling machine works. It is a short movie, but it shows the basics of operation of the machine.

Finally, we have another longer movie, where the person shows how he cut rifling using a rifling machine that he made from scratch by himself. While some of tools he used are a little more modern, it is interesting to note that most of the basic principles are unchanged. Interestingly, he marks his indexing guide free hand, instead of using a thread as we studied previously and his indexing head is merely a screw. His design is also a lot more compact and cuts handgun barrels.

Happy viewing.

Ancient Techniques of Rifling Machines - VIII

In the last seven posts of this series, we've looked at various parts of a cut-rifling machine, as was typically used by gunsmiths from the 16th century to a good part of the 20th century. As we have noted repeatedly in this series, the tools and techniques used to make the various parts of the machine were well known and fairly commonly available to people. The skills to make the various parts of the ancient cut-rifling machine were also known to carpenters, wheel-wrights, clock-makers and blacksmiths. In the early days of gun-making, blacksmith guilds worked in collaboration with carpenter and clock-making guilds to make firearms, before the advent of separate gunsmith guilds, which combined the skills of the other trades into their own specialized guilds.

In today's post, we will study how all the parts that were described in the previous seven posts, would have been combined together by an ancient gunsmith, to make a serviceable cut-rifling machine. The following diagram shows the assembled machine:

Click on image to enlarge. Image is not to scale. 

Author places the image in the public domain.

A few points to note: In the absence of modern lubricants, the ancient gunsmiths were known to use tallow or lard as lubricants instead. We already saw how tallow was made in an earlier post. Lard was made in a similar process (the main differences being, lard is made of pig fat, whereas tallow is made of beef or mutton fat and different parts of the pigs, cattle or sheep are used for lard or tallow as well). The rifling cutter tool would have been liberally coated with tallow or lard, to reduce friction and to cut more efficiently. Lard and tallow were also historically used in many cooking recipes (as a bit of trivia, McDonalds used to cook their fries in tallow until about 1990), so they would have been easily available to ancient gunsmiths.

In the above image, only two barrel clamps and two support blocks are shown. The actual numbers and positions of these could vary depending on the length of the barrel being machined. Also, the indexing guide is shown with only a single groove. In many cases, gunsmiths would cut multiple grooves on the indexing guide, so that errors in one groove would be largely cancelled out by the other grooves on the indexing guide.

As the head piece is pushed forwards and backwards, it causes the indexing guide to rotate at a fixed rate. This motion is transferred to the rifling cutter (which is inside the barrel) via the extension rod, to cut a rifling groove.

The ancient gunsmith would have first taken the barrel and made markings on the outside, corresponding to the number of grooves required for the barrel (or attached a larger indexing guide disc to the end of the barrel, with a number of markings/holes in it, corresponding to the number of grooves required in the barrel. By the way, if any of my faithful readers would like to know how to divide a circle evenly into 5 or 6 parts using only a straight edge and a set of compasses, please post a comment and I'll make a separate post for that). The gunsmith would have then mounted the barrel so that one of the markings aligns with a fixed marking on one of the barrel clamps or on a support block. The barrel clamps would have been tightened and then the gunsmith would have pushed and pulled on the head piece, until the cutting tool stops cutting. Then the gunsmith would have unclamped the barrel and rotated it to the next marking and repeated the process of pushing/pulling to cut the next groove and so on, until the required number of grooves were cut. Then, the gunsmith would have adjusted the cutting tool to increase the depth of cut (as described here) and repeated the process again, until the required groove depth was reached for all the grooves.

Person demonstrating a traditional rifling machine, as built in the Great Smoky Mountains region.

Click on image to enlarge. Public domain image.

The above picture shows a traditional rifling machine, as built by American backwoodsmen in the Great Smoky Mountains area between North Carolina and Tennessee. 

In the next post, we will study some pictures of the build process, as well as a couple of videos showing an ancient rifling machine in action. Until then, happy reading.

Ancient Techniques of Rifling Machines - VII

In our last post, we saw how ancient gunsmiths would have manufactured barrel clamps and the extension rod. In today's post, we will study the last few bits of ancient rifling machines and then study how they would have all been put together.

The first part is the supporting block. This is simply a block of wood that is used to support a barrel while the rifling is being cut. The simplest way to support a cylinder is to cut a v-shaped groove in a block of wood and the cylinder will be supported by the sides of the groove.

Click on image to enlarge. Public domain image.

Typically, ancient gunsmiths chose wood blocks made of pine or maple and simply carved out a v groove on top of each block, using a wood chisel and a mallet. The length of the V is made big enough to support a barrel through the groove. The gunsmith would have used two or more of these support blocks to support a barrel. In order to ensure that the support blocks don't move, the gunsmith would have either nailed the blocks or glued them into the proper positions on the machine. Another common technique used was to drill a couple of holes into the base of each support block and into the bed of the machine and use cylindrical wooden pegs to hold the support blocks in place.

The gunsmith could optionally also use C shaped strips of metal and screws to clamp the barrel to the support block. These could be used by themselves, or in conjunction with the barrel clamps we studied in the previous post.

The next part we will study is the bed of the machine. This is simply a long plank of wood, with holes drilled in specific places, so that the various other parts (such as the support blocks and barrel clamps) can be attached to it. As we saw in an earlier, mankind had already invented drills and reamers centuries ago, so these tools were easily available to gunsmiths in the 16th century. And as for ensuring that the surface of the bed is flat, the tools to do this were also invented by carpenters a long time ago. Ancient carpenters used a tool called an "adze" to make wood planks. Adzes have been known to exist since the Stone Age and were used by many cultures around the world (Egyptians, Mayans, Europeans, Indians, Chinese, Maoris, Polynesians, Hawaiians, Native Alaskans, Zulus etc.). Some time during the Roman era, the plane tool was invented to replace the adze and rapidly spread to several countries around the world. Examples of plane tools have been found in the ruins of Pompeii. Therefore, we can safely assume that gunsmiths in 1550 AD would have had access to good woodworking planing tools.

A Roman woodworking plane tool. Click on image to enlarge.

A modern planing tool made by Stanley Tools. Click on image to enlarge.

In the above images, we see two plane tools. The first one dates from the time that the Romans ruled England and the second one is a more modern version made by Stanley Tools. It is interesting to note the similarities between the two hand tools, considering that they are separated by almost two thousand years. The manual plane tool is only seen in small home workshops these days, as it has largely been replaced by the electric planers for quicker production.

Finally, our ancient gunsmith would have constructed a set of table legs to attach to the underside of the bed. Again, this is something that practically every village carpenter in Europe or Asia already knew how to build for thousands of years, so gunsmiths weren't inventing anything new.

In the next post, we will see how all these parts were assembled into a rifling machine that ancient gunsmiths used.

Ancient Techniques of Rifling Machines - VI

In our last post, we saw the different types of cutters used by various ancient gunsmiths on their rifling machines. In today's post, we will look at a couple of other parts of the ancient rifling machine that gunsmiths from centuries ago would have used as well.

The first part we will look at is the barrel clamp. Briefly, barrel clamps are used to hold a barrel while the rifling is being cut on the inside of it. We will look at a common design that was used for this purpose. A typical ancient rifling machine would have had at least two or more clamps of this type to hold down the barrel.

The first part of the barrel clamp is the clamp ring. This was typically made of a thin flat ribbon made of iron or steel, which was bent into a ring shape, as shown in the figure below:

Click on the image to enlarge. Not to scale. Author places the image in the public domain

The clamp ring's inner diameter is slightly larger than that of the barrel it is expected to hold. The ring does not form a complete circle, but has a small gap at A.

The next part of the barrel clamp is a pair of flanges, which were usually forged out of iron or steel. A diagram of these is shown below:

Click on image to enlarge. Not to scale. Public domain image.

Basically, these are just flat pieces of metal with holes punched in the middle. Each barrel clamp requires two of these.

In addition to these parts, the gunsmith would have built a small bolt to hold the flanges together and a larger bolt to hold the entire clamp. This would have required skills in cutting screw threads and making nuts and bolts, but these were technologies that were already mastered for hundreds of years.

An assembled barrel clamp is shown below:

Click on image to enlarge. Not to scale. Author places image in the public domain.

The gunsmith would have welded the two flanges to the end of the clamp ring at A. A small bolt is passed through the holes in the two flanges and a nut fastened to the other end. The clamp ring can be then tightened or loosened around the barrel by turning the small nut at A.

A larger bolt is welded on to the clamp ring at B. The other end of the larger bolt has two large metal washers and nuts. When attaching the clamp to the machine's bed, the lower nut and washer are unscrewed from the bolt and it is passed through a hole drilled on the bed and then the lower washer and nut are screwed back on to the bolt and both nuts are tightened to the surfaces on either side of the hole, to firmly attach the clamp to the machine bed. This design allows the gunsmith to raise or lower the barrel clamp as needed. The gunsmith would have used two or more of these clamps on the machine's bed to secure the barrel. We will look at how these would have been positioned in a couple of posts.

The next part that an ancient gunsmith would have made for this machine is the extension rod. Basically, it is simply a long rod that connects one end of the indexing guide to the end of the rifling cutter.

Click on image to enlarge. Not to scale. Author places image in the public domain.

The rod is made of either wood or metal and each end has a metal wood screw attached to it, either by welding or brazing them on. One end of this rod is screwed into the wooden indexing guide and the other end is screwed into the wooden part of the rifling cutter.

As you can see, any ancient gunsmith with good woodworking and metalworking skills would have easily been able to make these parts. The only remaining parts of the machine left to study are some wooden parts like the bed, the legs and the support blocks. These are not complicated parts, but are some of the largest parts of the machine. We will study these in the next post and also see how the machine is assembled in the next couple of posts.

Ancient Techniques of Rifling Machines - V

In our last post, we saw how an ancient gunsmith would build the head piece and tail piece and assemble some of the parts of the manual rifling machine. In today's post, we will deal with another important part of the machine, the rifling cutter.

Briefly, the rifling cutter is the part that actually cuts the grooves on the barrel. There were several designs of rifling cutters over the ages and we will study some of the common variants in today's post. First, we have the actual cutting tool. This was usually made of forged steel, with one or more sharp cutting edges. Once the sharp cutting edge was formed, the gunsmith would harden the cutting tool using the same heat treatment techniques that were known to sword smiths.

A cutting tool. Click on image to enlarge. Author places image in public domain. Not to scale.

In the above image, we see a cutting tool with two teeth. A cutting tool could have a single cutting tooth or multiple teeth, depending upon the gunsmith's desires.

This cutting now needs to be mounted to a cutter body, so that it can be used in a rifling machine. The simplest rifling cutters had the bodies made of wood. The gunsmith would first use a lathe to make a wooden cylinder out of a hard wood (such as oak or hickory), a little less than the diameter of the barrel to be rifled. Then the gunsmith would chisel out a slot on the top of the cylinder, just big enough to insert the cutting tool into the slot. The gunsmith would then insert the cutting tool into the slot and add glue to fasten the tool to the cutter body. Finally, as an optional extra precaution, the gunsmith would also wind some wet twine around the cutter body to overlap the tool's body. As the twine dries up, it tightens around the wood and secures the cutter extra-tightly to the body.

A simple rifling cutter. Click on image to enlarge. Author places the image in the public domain. Not to scale.

The above image shows how ancient gunsmiths would construct such a cutter. The advantage of this type of cutter is that it is relatively easy to construct. However, the height of the groove cannot be adjusted easily with this type of cutter. The solution is to adjust the barrel's position to deepen a groove and we will study that when we look at barrel clamps. In other cases, the gunsmith would simply move the cutter back and forth until it cut the groove to the required depth throughout the length of the barrel.

A slightly better modification to the above design was also used by ancient gunsmiths. The gunsmith would construct a wooden cylinder out of oak or hickory, using a lathe. Unlike the previous cutter body though, this one would have a thicker cylinder in the center and two smaller cylinders at the end. Then, the gunsmith would split the cylinder into two pieces lengthwise and then carve out a long groove on each of the halves. The gunsmith would then attach the cutting tool to one of the pieces and then glue the two halves back together and secure the ends with twine or tight leather bands. In the gap between the long grooves, the gunsmith would force two tight fitting wooden shims in, before gluing the two halves together. The image below shows how this was done:

Ancient Rifling Cutter. Click on image to enlarge. Author places the image into the public domain. Not to scale.

In this type of cutter, the gunsmith can move the cutting tool down or up by moving the two shims closer to or away from the center of the cutter. Alternatively, the gunsmith can add more padding material into the center gap to raise the cutting tool. This type of cutting tool was commonly used by ancient gunsmiths, but the depth of cut cannot be set very precisely by moving the shims.

Another more advanced cutter design that allowed gunsmiths to precisely set the depth of cut of the grooves was also used. To make such cutters, gunsmiths needed access to techniques to cut precise screw threads and make springs. These technologies were already known and perfected by clock manufacturers, so gunsmiths in areas that were famous for clocks (such as Nuremberg in Germany) took advantage of their knowledge to make a better rifling cutter.

The cutting tool in this case, has a hole drilled in it, through which a pivot pin may be passed. There are two threaded bolts (one for each end of the tool), one wedge shaped metal part, another metal block and a spring, as shown below:

Click on image to enlarge. Author places image in the public domain. Not to scale.

The ancient gunsmith then makes a hollow metal tube, with an inside diameter that is slightly larger than the wedge's height. Screw threads are cut on the inside of each end of the metal tube. The gunsmith then drills a hole across the tube to fit the cutting tool in and cuts a large slot on top for the cutting tool to protrude through, as shown in the image below:

Click on image to enlarge. Author places the image in the public domain. Not to scale.

In the above image, A and D are the screw threads that are cut on each end of the tube. C is the hole drilled across the tube, through which the cutter will be fitted to the case with a pivot pin. B is the slot cut on the top of the tube, that allows the cutting tool to protrude through.

The parts are then assembled into the cutter case tube, as shown below:

Click on image to enlarge. Public domain image. Not to scale.

By rotating the threaded bolt on the left side, the gunsmith pushes the wedge in or out of the tube, which forces the cutter to rotate about the pivot pin and protrude higher or lower out of the slot B, which adjusts the depth of the groove to be cut. The metal block and spring push against the cutter and keep it from rotating from the other side. With this type of cutter, it is possible to set the depth of cut very precisely by rotating the bolt on the left side. This sort of cutter design was used by gunsmiths for a very long time, all the way to about World War II. In fact, we discussed this type of cutter way back when we studied cut rifling techniques almost four years ago. There are still some gunsmiths using such cutter designs today.

Rifling cutters. Click on image to enlarge.

The above image shows three rifling cutters of this design. You can clearly see that each cutting tool is attached to its case using a pin. You can also see the wedges and threaded bolts on the right side of each tool.

In this post, we have covered how the cutting tool was made throughout the ages. In the next couple of posts, we will study how the cutting tool was attached to the indexing guide and also study how the rest of the rifling machine was built.

Ancient Techniques of Rifling Machines - IV

In our last post, we saw how an ancient gunsmith could have built an indexing head and in the post before that, we saw how they could build an indexing guide. In todays post, we will look into how they would mount the indexing guide and indexing head together, along with the head piece and tail piece.

As we noticed in the post for the indexing guide, the cylinder is mostly about 4" in diameter, except at the ends, where the diameter is 2" or 3" on either end.

The ends are where we will mount the head piece and tail piece. First, we look at the head piece.

The Head Piece. Click on image to enlarge. Not to scale.

Author places the image in the public domain.

It consists of a rectangular board of wood in which a few holes are drilled or chiselled out. Holes A and C are rectangular holes which are identical in dimensions. Hole B is a circular hole which is drilled to the diameter 3" (i.e.) the diameter of the cylinder at the right end of the indexing guide. It must be noted that the distance between the holes A and C must be greater than the width of the indexing head that we studied in the previous post. We will see why shortly. Finally, the gunsmith attaches handles on either side of the head piece.

Next, we look at the tail piece.

The Tail Piece. Click on image to enlarge. Not to scale.

Author places the image in the public domain.

In this piece, there are two notches A and C, which are to identical dimensions of A and C in the head piece above. The distance between A and C is also exactly the same as between A and C in the head piece above. The hole B is drilled to a diameter of 2", or exactly the diameter of the cylinder at the left end of the indexing guide. Finally, we have a large section D, which is the width of the bed of the indexing machine. We will see how this all fits in the next few images.

The gunsmith takes two long pieces of pine wood which are 1 inch x 2 inch in cross-section and about 50 inches long and attaches them to holes A and C on the head piece and tail pieces, using glue and nails. These long pine pieces act as braces and connect the head piece and tail piece together He also slips in the indexing piece into holes B on the head piece and tail piece. The figure below shows how the tail piece attaches to the indexing guide:

Tail piece assembly. Click on image to enlarge. Not to scale.

Author places the image in the public domain.

The next image shows how the head piece, tail piece, indexing head and indexing guide are all attached to the bed. First, the gunsmith selects a long plank of wood as the bed of the machine. Then he attaches the indexing head to one end, using nails or screws to secure it. Then he screws in the indexing pin  to the indexing head and passes the indexing guide through the hole. Then he attaches the head piece and tail piece to either end of the indexing guide and then connects the wooden braces to the head piece and tail piece. Note that the section D on the tail piece is wide enough to slide on top of the bed of the machine. The assembly so far looks something like this:

Assembly of the manual rifling machine. Click on image to enlarge. Not to scale.

Author places the image in the public domain.

The gunsmith can now grab the two handles on either side of the head piece and slide it back and forth along the bed. As the head piece and tail piece slide along the bed, the indexing guide also moves along with them. Due to the groove in the indexing guide meshing with the indexing pin on the indexing head (which is fixed to the bed and does not move), the indexing guide rotates at a fixed rate, equal to the groove's twist rate (which we saw how to machine, two posts earlier).

In the next few posts, we will see how our ancient gunsmith could have fashioned a cutting tool and attached it to the indexing guide and also see how the rest of the machine is built. Happy reading!

Ancient Techniques of Rifling Machines - III

In our last post, we saw how a gunsmith from hundreds of years ago, could construct an indexing guide, a key part of a manual rifling machine. In today's post, we will study how they could make the indexing head, another key part of the machine. Like the indexing guide, the indexing head is also constructed as accurately as possible.

The purpose of the indexing head is for the indexing guide to pass through. This is the part that serves to rotate the indexing guide at a precise twist rate, which is in turn, used to move the cutting tool inside the barrel and cut the rifling grooves. Here's what the indexing head looks like:

Click on image to enlarge. Author places the image into the public domain. Some dimensions are not to scale.

The gunsmith starts with a flat plank of wood of suitable size. The gunsmith then bores a large hole B in the plank, to a diameter slightly larger than the indexing guide that we studied in the previous post. In the previous post, we had decided that the indexing guide had a diameter of 4 inches at its thickest part. Therefore, the diameter of the hole B is drilled to about 4.25 inches, so that the indexing guide can fit through this hole with a bit of clearance.

After that, the gunsmith chisels a hole at one edge of the hole B, so that he can screw in a small indexing pin A. The indexing pin A can be made of steel, brass or any hard wood such as oak, maple etc. The material is simply cut from a blank using a hacksaw blade and then filed into shape, and a hole is drilled in the middle to support a screw. The indexing pin is made long enough to fit in the groove that was cut in the indexing guide we saw in the previous post.

Building the indexing pin. Drawing is not to scale. Click on image to enlarge.
Author places the image in the public domain.

The indexing pin is inlaid into the indexing head, so that it cannot move at all.

The gunsmith also drills three or four holes C, at the bottom of the indexing head, so that the indexing head can be attached to the rifling machine bed via screws through these holes.

The indexing head mates with the indexing guide from our last post, as shown in the image below:

Drawing is not to scale. Click on image to enlarge.
Author places the image in the public domain.

The indexing head is fixed to the bed of the rifling machine and the indexing guide is pushed through it. The indexing pin fits into the groove of the indexing guide and causes the guide to rotate at a fixed rate, as it is being pushed or pulled through the head.

Of course, the curious reader might ask, how does a person drill such a large hole like B into a plank of wood. Luckily for us, the tools to do this were already invented and perfected several hundreds of years ago. Remember that mankind has been using the wheel for thousands of years and the wheel is attached to the axle with a relatively large hole. The first solid wheels and axles began to appear in Mesopotamia, Central Europe, Balkans and Northern Caucasus around 3500 BC. By about 3000 BC, the Indus valley civilization in Northern India shows evidence of having spoked wheels. By 1200 BC, chariots with spoke wheels were known to just about everyone in Europe and Asia and parts of Africa as well. Therefore, the technology for boring large holes into objects (e.g. for attaching an axle to a wheel and attaching spokes to wheels) was pretty well developed by this point in time. Tools such as the bow-drill and gimlets could be used to drill smaller holes and then the holes could be enlarged by using augers and reamers.

A Bow Drill

An Auger. Click on image to enlarge.

Several examples of Reamers. In particular, note the one from Roman times. Click on image to enlarge

A wheelwright using boring tools to fit an axle to a wheel. Click on image to enlarge,

While the images above show the tools used by a wheelwright to bore a hole into a wheel for an axle, the same tools and techniques were also used by ship builders, architects, carpenters etc. Therefore, it is a pretty safe bet to say that a gunsmith in 1500 AD had the tools and knowledge to easily bore a large hole into an indexing head.

The parts in this post and the previous one need to be built as accurately as possible, to produce good rifling. In the next few posts, we will study some of the other parts needed to build the manual rifling machine.

Ancient Techniques of Rifling Machines - II

In our last post, we started a series on studying how people used to cut rifling in their barrels manually, without the benefit of modern machinery. In our last post, we left off with the study of an important woodworking and metalworking tool, the lathe. As we saw in our last post, lathes were available to various cultures around the world, since the times of ancient Egypt, so it is pretty reasonable to assume that they were available to people around 1500 AD as well.

In today's post, we will look into the construction of an indexing guide. This is basically the part of the rifling machine that twists the cutting tool at a fixed rate, so that it cuts the required rifling grooves inside the barrel. This is the one part of an ancient rifling machine that needs to be as accurate as possible. Of course, we will first study how they built the most complicated part, so that the rest will appear a lot easier!

As we studied in our previous post, lathes can be used to make cylindrical shapes. The workman simply mounts a log of wood on his lathe and starts turning it and applies a sharp tool to the side of the rotating log to carve out a cylinder. So our ancient gunsmith would have used a lathe to carve a wooden cylinder made of oak or maple, about 4 inches in diameter and at least 50 inches long (assuming that he wants to make a rifled barrel with a twist rate of 1 turn in 48 inches, which is a typical twist rate of that era, so he makes the cylinder at least 48 inches long, with a little bit extra), with smaller protruding cylinders at either end of the log, such as the illustration below shows (please excuse the crudeness of the drawing :)):

Click on image to enlarge. Author places this image in the public domain,

The next thing to do is inscribe a groove on the thickest part of the cylinder (i.e. the part that is 50 inches long). The groove will help guide the cutting tool at the required twist rate.

The groove forms a helical path on the outside of the cylinder. So how did people build this in the middle ages. Luckily for us, there is a simple way to do this, which has been with us since ancient times. First, the gunsmith draws two sides of a right triangle ABC on a flat surface as follows:

Two sides of a right triangle. Clck on image to enlarge

Here, AB is 48 inches long (because we wanted a twist rate of 1 turn in 48 inches) and the length of side BC is equal to the circumference of the wooden log that was just shaped. The gunsmith can calculate the length of BC to be (pi * diameter of the cylinder), or the gunsmith can simply measure this out by wrapping a thin thread around the surface of the cylinder and marking it, then placing the thread on the line BC and measuring out the length of the markings. The only trick is ensuring that the angle ABC is a right angle (i.e. 90 degrees) and as we will see, measuring this out is a piece of cake as well.

Sidebar: How to measure a right angle

This might be a good time to talk about how people measured right angles back in the day, if only for the reason that such knowledge of geometry is gradually being lost today unfortunately. Today, any student can buy a protractor at any stationary shop for a couple of dollars (A 10 piece Staedtler mathematical instrument set cost me $3.99 and it contains a protractor, two set squares, a compass, pencil sharpener, pencil, a ruler etc.). However, a protractor wasn't in common use before the 19th century and such instruments were generally more expensive before the 19th century and weren't easily affordable to ordinary smiths. So let us only consider instruments that were cheap and widely available for that era.

As it turns out, ancient civilizations like the Egyptians and the Chinese had already developed set squares, way back in the day (Egyptians seem to have had them as far back as 1300 BC or so), so they were probably widely available to various people in the middle ages as well. While you can't measure any angle with a set square like you can with a protractor, they can be used to measure right angles very well.

Ancient Egyptian set square from 1300 BC.

The above instrument is from ancient Egypt and such instruments were known back in the time of the Pharoah Ramses and used by them to build pyramids, so they were definitely widely available in many countries by the middle ages. Using one of these instruments, a gunsmith could have easily drawn a right angle.

The other ancient mathematical instrument is the compass, which was also known to ancient civilizations like the Greeks, Chinese, Indians, Romans etc. For example, Euclid's classic mathematical work Elements from around 300 BC mentions compass and straight-edge problems in book II of the series, and a classic Chinese mathematical text, the Zhoubi Suanjing from around 100 BC, also mentions the use of set square and compass in geometry problems. Ancient compass instruments have been found intact in the ruins of Roman cities like Pompeii and ancient Indian mathematical texts also talk about usage of such instruments.

A set of bronze compasses from the Roman era

Even if a person has no compass, he can still improvise with two sharp objects (e.g. two pencils) and a ribbon connecting the two sharp objects together at a given length. As we will see below, we can still draw a fairly accurate right angle with such a crude instrument, using the procedure below:

Say we have a line AB and we wish to draw a right angle at point B. Imagine that the only instruments that the gunsmith has available are a straight edge and a compass (and if he doesn't have a compass, he has improvised by tying two pencils, one on each end of a shoe lace!). The first thing to do is to mark the point B and then use the straight edge to extend the line AB beyond the point B, as shown in the illustration below:

Then, he opens his compass (or his crude shoe-lace and pencil contraption) to any convenient length and using B as the center, he draws two arcs on either side of B to mark out C and D as shown below:

Now, he opens the compass out a bit so that it measures out any arbitrary distance greater than BC (it can be greater than CD also, it doesn't matter). Then using point C as the center, he uses the compass to draw an arc above line AB as shown in the image below:

Then, using the compass set to the same length as the previous step and using D as the center, he draws another arc above line AB, that intersects the previous arc at point E, as shown below:

Now, he uses the straight edge to connect points B and E together in a straight line as shown in the figure below:

 Voila, angle ABE is a right angle and it has been drawn without any sophisticated (for that time) instruments at all.

Now back to topic...

Now that we know how to construct a right angle with simple tools, we go back to our original figure ABC, where line AB is 48 inches long and BC is the diameter of the wooden log that the gunsmith intends to use as an indexing guide. The gunsmith then uses a ribbon or a thread dipped in glue to connect points AC, such as in the figure shown below:

Then, the gunsmith places the indexing cylinder guide so that it is touching AB and rolls it up, so that the sticky thread on AC gets wound on the outside of the cylinder. Instead of using sticky thread, the gunsmith can also mark AC with a dark charcoal marker, so that the marking gets transferred to the indexing cylinder when the cylinder is rolled on it. The procedure is shown below:

Now that the cylinder is marked properly, the gunsmith can use a sharp chisel and mallet to cut a groove along the path marked by the sticky tape. Voila, the groove is produced at the desired twist rate and we have our indexing guide, as shown in the image below:

The indexing guide was actually one of the trickiest parts that the gunsmith needed to manufacture for his manual rifling machine. As you can see, even in the middle ages without access to any sophisticated modern tools, it was possible for a skilled workman to construct an indexing guide pretty accurately.

In the next post, we will look at the next part that needs to be constructed relatively accurately, the indexing head and pin. Then we will look at how the remaining parts were built and how the machine was assembled in subsequent posts.

Ancient Techniques of Rifling Machines - I

In the last few posts, we studied some videos of rifling techniques and we had also studied the descriptions of these techniques in detail many months earlier. The thing to note though is that all these videos showed relatively modern machinery making the rifling. In fact, the oldest machine in those videos dates to some time in the early 1900s. However, as we have seen earlier, the history of rifling dates back to about 1520, well before such automated rifling machines were invented. So how did people historically cut rifling grooves into their barrels, without the aid of modern machinery? We will attempt to reconstruct their techniques in the next series of posts, only using technologies that would have existed in the 1500s and 1600s. As we are studying the techniques, it will become fairly obvious to the reader, that historical gunsmiths would have had some pretty good skills in both woodworking and metalworking, which is why they formed separate gunsmithing guilds, which were different from carpentry and blacksmith guilds.

The first tool that any gunsmith would have used would have been a lathe. This handy tool was known to the ancient Egyptians in 300 BC and later spread to the Greeks, Indians, Chinese, Assyrians, Romans etc. The first design simply had one person alternately pulling on two ends of a rope looped around a wooden work piece, to rotate the work piece around two centers, and the other person would apply a sharp edged tool to the rotating wooden piece, to cut it into a cylinder or a tapered cylinder or a similar shape.

The following image can be found in a bas-relief carving at the tomb of Petosiris, a high priest who lived in Hermopolis, Egypt, dated to about 300 BC.

Two images of lathes, as used in ancient Egypt

The basic two-person operated lathe concept was modified by other cultures, as shown in the example from India below:

Horizontal two person lathe used in Ancient India.

The Romans came up with a lathe design that used a bow to turn the wooden work-piece. With this type of lathe, there is no need for a second person, as a single person can move the bow with one hand and manipulate the cutting tool with the other hand. However, there is lesser power applied, since the person is turning the work piece with only one arm and hence it is suitable for smaller jobs only.

The bow lathe design stayed with us for quite a long time: small bow lathes were still used by clockmakers in the early 1800s.

In the middle ages, someone got the idea of tying one end of the rope to a thin springy pole or branch and the other end to a foot pedal and the rope would loop around the wooden work piece to be turned. The craftsman would use his foot to operate the pedal and use his two hands to hold various tools against the turning wood piece.

Spring pole lathes from the middle ages

The above illustrations show some spring pole lathes from the middle ages. The left side illustration is based on a Parisian manuscript from the 13th century. As with bow lathes, spring pole lathes do not need for a second person to turn the wood piece. Spring pole lathe designs were commonly used for hundreds of years, all the way to the early part of the 20th century!

Other lathe designs included using horses, flowing water, steam and electricity to power them and lathes evolved to cut both wood and metal pieces.