How rifling is made in barrels. How it's made, how it works, how it works
Rifled barrels appeared more than 600 years ago, but, oddly enough, many of the principles that the gunsmiths of the Middle Ages understood are still relevant today. Technologies have changed, new control methods have appeared, new steels have appeared, but the principle of operation of ultra-modern computer-controlled equipment is the same as that of an ancient wooden bore cutting machine made by a 15th century barrel maker.
What is a rifled barrel?
Essentially, the barrel is a pipe with rifling inside. The rifling is made at an angle to give the bullet a spin, an angular velocity that will stabilize it in flight. The same principle is implemented in the spinning top toy, which can maintain a vertical position only by rotating.
First, a few terms: bore size is the bore diameter along the fields, grove size is the diameter along the rifling. The .308 Winchester bore size is .300 inches (or almost exactly 7.62mm), and the grove size is .308 or 7.82mm, which is the same as the lead diameter of the bullet for this caliber.
In Russia, the 7.62 caliber has an actual size of 7.92 (by rifling) or .311 inches.
The barrel is a very difficult part to manufacture. Here all the equipment and technology with the prefix “special” - special machines and tools. The barrel path begins at a metallurgical plant where special steel rods are manufactured. In the US, this is usually 416R stainless steel, nickel-free steel, or 4140 chrome-molybdenum steel.
In Europe, they use their own specifications, and although they are quite close, there are still differences, for example, Lothar Walther stainless steels are harder than 416R and closer in composition to 420 steel.
After manufacturing and cold forging, the barrel steel rods are subjected to surface treatment (turning or grinding) and heat treatment to relieve stress.
In the barrel production, the rod is cut into measured pieces with a band saw, after which it is placed in a special machine for deep drilling. Drilling is considered deep when the hole depth is more than 10 diameters.
In barrel drilling, this ratio is usually equal to or more than 100. It is clear that such a complex operation can only be done with a special tool. The barrel drill is an amazing tool. It has one blade and looks like a crescent, only the inner sector is chosen as an angle. It has a complex sharpening shape, determined using special tables.
There is a hole inside the drill for oil supply. Oil washes out chips through the drill, lubricates and cools the metal in the cutting zone. An important feature of deep drilling is that during this operation the workpiece rotates, but the drill is stationary and feeds only in the longitudinal plane at a speed of about 3 cm per minute. It usually takes about half an hour to drill a barrel.
After drilling, the future trunk is checked for center-to-center deviation; if at the point where the drill exits the deviation is more than 0.3 mm from the center, then such a part is rejected.
The next operation is drawing the reamer. The multi-blade tool rotates and is pulled through the bore, removing drill marks and providing the barrel with a nearly polished interior surface. Next, the barrel bore is additionally honed or polished.
After this comes the most difficult and crucial moment - making the rifling.
Currently, five main methods are used for cutting the bore: this is a single-pass cutting; mandrel pulling; rotary forging; multi-blade broaching; electroerosive method.
In target shooting, only lorning and single-pass cutting are used; all other methods make it possible to produce only mass-quality products.
Mandrel pulling as a method of profiling the bore appeared in the 40s of the last century. This method was mastered almost simultaneously by German and American gunsmiths and was a kind of
a technological breakthrough, since the method is simple both in execution and in the required machine park.
The mandrel is a carbide head that follows the final contour of the barrel with fields and rifling, but is slightly larger. The mandrel is installed on the rod, the rod is passed through the barrel, the shank of the rod is secured in the tool holder and pulled through the barrel, the pressure of the mandrel on the walls of the hole forms the rifling.
The first secret of this technology is the lubricant that is used when pulling the mandrel. The classic method is copper plating of the barrel. In this case, the lubricant is copper, the mandrel slides over it without effort. However, applying it to the bore is a labor-intensive process. Now many have begun to use their own lubricant formulations developed on the basis of modern antifriction compounds. In any case, this is the “know-how” of highly qualified gunners.
The pitch of the rifling is set by a special mandrel - a copier. On it, the grooves seem to be turned inside out, on the outside. They set the angle of rotation of the mandrel to the desired pitch, moving along special guide bushings. The operation is quite fast and requires about 5-6 minutes of time, including installing the part into the machine. However, since the dimensions of the mandrel are larger than the desired caliber, after the operation it is necessary to carry out a heat treatment procedure to relieve stress. During this treatment, the barrel will “shrink” to the required size, and stress will disappear - stress that has arisen in the metal due to the enormous pressure of the mandrel.
This is where the main secret of the trunkers arises, which lies in the temperature conditions of processing and holding time. The slightest error in the modes will lead to the fact that the barrel will begin to shrink during shooting. In addition to the fact that it is definitely impossible to shoot from such a barrel, it is also not safe, since enormous pressures arise at the moment of firing, which can lead to the rupture of the cartridge case or the jamming of the bolt.
Tool for forming rifling in the bore using the mandrel pulling method
Dormant barrels have dominated benchrest competitions for a very long time. The “eternal” record of Pat McMillan was set from a barrel he made himself and is equal to 0.009 MOA (five shots at 100 yards). Pat built a pull-through setup in his garage using very simple tools and achieved impressive results.
His trunks (and he made very few of them, only about a couple of hundred) are considered the standard of this production method.
In the 80s and 90s, the Shilen company became the market leader; several dozen world records were set with their trunks. The great Tony Boyer won all his early titles using these barrels. And then something strange happened: Shilen barrels began to shoot worse, and the reasons are still unclear. There is a version that this is due to errors in heat treatment (new furnaces with increased capacity were installed), and it is possible that other batches of steel were used. But the fact remains that today Shilen is a rare guest in the equipment list of top Shooters.
In the mid-90s, the leadership was seized by companies producing barrels using the single-pass cutting method (in Russian terminology it is called hook trellis planing). This method is called single-pass not because the groove is formed in one pass, but because the tool makes a working stroke in only one direction. The method is much more complex and very demanding on the skills of the performers. The essence of the method is that a small cutter (in the English version “hook”), installed in a special mandrel, stretches through the barrel and cuts off a micron layer of steel, forming a rifling in several dozen passes. The method is very slow; it takes about two or more hours to make one barrel. The incisors are very small, and the number of craftsmen in the world who can make them with their own hands can be counted on one hand.
However, the result is excellent. A striking feature of this production method is that all the machines that are used in the world to make barrels using this method were manufactured by the English company Pratt Whitney until the 50s of the last century. These are mechanical machines, no electronics, completely manual control.
The leader of that period was the Kriger company. John Krieger has assembled an incredible team of top-level specialists. They were the first to modernize their equipment, adding digital rulers and CNC systems to old machines.
Krieger would continue to remain the market leader, to which not only athletes and hunters, but also large companies, for example, the legendary Barrett, stood in line for barrels for six months or more. However, Krieger did one thing that he probably still deeply regrets: he fired his best specialist, Tracy Bartlein.
In 2004 Bartlein created his own company - this is how a story began that fully fits the definition of the “American Dream”. A new and unknown company began to produce barrels of such quality that it came as a shock to many. As soon as athletes and gunsmiths “tasted” what Bartlein offered them, orders simply came in an avalanche. Today, dozens of world records have been rewritten with Bartlein barrels, and equipment lists at all major competitions are filled with this name. Barrett terminated its existing contract with Krieger, paying a penalty, and entered into a new agreement with Bartlein. Remington and Accuracy International install Bartlein barrels on their most expensive tactical models.
The reason for this phenomenal success is that Tracy spent two years creating a special CNC machine for cutting the bore.
When it was made, the accuracy of the tool improved by an order of magnitude, in addition, today Bartlein is the only company in the world that can produce barrels with variable rifling pitch. Computer control and total quality control make it possible to obtain champion-quality barrels in large quantities. It should be noted that Bartlein is the only manufacturer who does not have a selection of trunks; he only has them of the highest level.
Olga Gulidova
In this master class I'll try to describe how I do it trunks for your trees made of beads. First theory, and then practice.
Theory
If used as a material for the barrel plastic, then I use it like regular plasticine. Using a stick (toothpick or sharpened wire), I apply a bark-type pattern to the trunk using pressure of varying strength, and then follow the instructions for the plastic.
To make a barrel I use and a mixture of alabaster and PVA glue.
Consistency can be different and the texture of the trunk depends on it. I apply it to the bare wire frame of the tree, without first thickening it with different materials. From experience, when using them, the trunk cracks when the mixture dries (not always, but often). So for me it's better to apply more mixture than to regret the appearance of cracks. First, you can knead the mixture thicker. It is used to form just that thickening of the trunk. The mixture does not flow and dries faster. But the mixture dries very quickly, so you need to apply it as quickly as possible. Usually, in the first stage, I apply only to the trunk itself and mainly at the base, creating almost the desired thickness of the trunk (there will be another layer on top, the so-called bark). Then the mixture is diluted to be more liquid. While it is quite liquid, I quickly apply it with a thin brush to thin branches that need to be slightly thickened or smoothed out at the junctions. The thinner the mixture, the smoother the surface will be when dry. This is what we need on the branches. As the mixture thickens, I coat the branches closer to the trunk and the junction of thick branches with the trunk. And with a thicker mixture I already form the tree bark. In this case, the mixture should have the consistency of butter if it had been taken out of the refrigerator an hour ago (oh, I compared it :)) I just want to say that a liquid mixture will not lie down as it should, but a very thick mixture will fall out in chunks. With the required consistency, the mixture itself lays down as needed, in the form of a bark.
For work I use wide synthetic brush, she's tough. It’s even better to have thin ones on hand pointed sticks(toothpick, wire) to use for drawing the bark, if necessary. Usually the barrel takes at least an hour. Some people cast magic for 4 hours. This is a matter of taste, experience, desire and pleasure (not without this;)).
After the barrel has dried, you can touch it up (if necessary) nail file nail polish (I have an old artificial nail file for this purpose) or fine-grit sandpaper.
Painting a beaded tree trunk- that’s a different story :) I sometimes repaint my trees 5 times until I achieve what I wanted.
First coat of paint - basic. This is the color of future cracks in your bead tree. Paint on top with a semi-dry brush (hard or soft, too, because the effect is different) with the color you expect to see. trunk. You can also use several shades for shading the trunk. I get shades by mixing primary colors.
After the paint has dried, do you cover it or not? varnish, to your taste. I cover it matte.
Practice
The first thing you need is a finished bead tree put in plaster.
To prevent the pot from cracking, there are several options: add sand or fine expanded clay to the solution, you can put pieces of cocktail tubes before pouring. You can also put small pieces of crumpled foil on the bottom. It is better to pour it in layers, first placing the tree firmly, propping it up, for example, with books.
The pot cracks due to the expansion of the mixture when it dries, so you need to take care of the reserve of this expansion (the tubes or foil will be compressed, and the pot will not crack).
Collected twigs in heaps so as not to interfere.
Prepared tools so that everything you need is at hand.
Likewise, there should be the necessary people nearby materials.
IN equal proportions mix plaster...
... and PVA glue.
The result was a slightly thick mixture. Don't do more, it sets very quickly!
Apply the mixture to the trunk.
Thickening the trunk to the desired size in one or more approaches as the mass dries.
Coat thin branches with a thinner and less thick layer of the mixture.
As it dries, use a stick to spread the mixture over the surface of the trunk and it will lay down texturedly, like tree bark.
Can toothpick add a stripe if you want.
I decided to apply the first coat of paint from a cylinder, so I covered the branches with foil.
Result wood staining at this stage.
The project to build a factory for the production of rifles arose quite recently in 2008, and the first product was released just two years ago in March 2011. The plant was built almost from scratch; initially, in its place there were premises in a terrible state. On May 15, 2010, the overhaul began. The production flagship - the ORSIS sniper rifle - is an abbreviation for the phrase “weapon systems”. But we will return to the history of the plant, and now let’s go inside.
My path passes through the workshop where barrels are processed. The workpiece in which the hole will be drilled and the cutting will be done is called a “blank”. The forms are supplied to the factory from the USA.
Parts for rifles are processed on such machines. Here, a hole is first drilled in the blanks, the width of which depends on the caliber of the future rifle. By the way, some machines were designed in the plant’s design bureau with the assistance of consultants from Switzerland and Germany.
In general, the plant has more than 30 computer numerical control (CNC) machines for various purposes. They are very different, some are simpler, for simple operations, and there are also those that do truly unique things, using technologies that I heard about for the first time.
The barrels are made of special weapons grade stainless steel.
Pay attention to the coin. It stands edge-on on the moving part of the machine, which cuts the barrel from the inside. The smoothness and accuracy of the move during this operation is so high that it does not allow the coin to fall. At the end of the post you can see a video of this process.
The same machine. Here you can see how the rod goes into the barrel blank, making the rifling - 4-6 spiral strips, they help stabilize the trajectory of the bullet. The cutting is done with a specially shaped metal hook, which is also manufactured at the factory.
The tool enters a stationary workpiece and leaves a cutter mark one micron deep. To make cutting easier, oil is poured onto the barrel. The process of cutting a barrel lasts 3-5 hours. For one cut, the tool must go inside 60-80 times. After this, the barrel is manually polished with a lead-tin lap and cleaned of oil.
After these operations, the trunk goes to the laboratory.
Here, specialists probe the bore with a borescope (a relative of the endoscope) for defects - scratches, pits or cracks. The barrel is checked several times: after drilling the hole, cutting and polishing.
We will find out what kind of firewood this is a little later.
A blank that will soon become the main part of the bolt mechanism.
A CNC machine processes a part of the shutter mechanism, which is immediately cooled with water.
General plan of the second workshop.
Each model has its own stock. It provides rigidity to the structure. For tactical rifles they use a stock made of aluminum, for sports rifles - from a special weapons laminate. In addition, the factory makes a custom-made stock from valuable types of wood, such as walnut.
The machine also operates on program control.
One blank of this part can cost several tens of thousands of rubles. If you look closely at one of these bars, you will notice 4 layers of plywood or, as it is otherwise called, wood laminate.
After processing on a milling machine, craftsmen manually grind it, apply signature notches with a laser and impregnate it with oil several times. During one shift, the master makes 2-3 beds.
A recess is made in the blank for the barrel, after which it is once again coated with oil and then varnish.
Here you can see how the workpieces are polished.
And in the next room a small discovery awaited me.
Here, using high-precision equipment (the cost of which amounts to tens of thousands of euros), parts for the bolt group (hammers, safeties, triggers) are cut out of metal, which would be impossible to make using other machines.
The parts are cut using electrical erosion technology. This thread, it can be made of molybdenum or brass.
It all happens like this: the thread from the spool is passed through a small hole in a metal sheet or blank, secured from below so that it can be wound onto another spool. This sheet is then immersed in a bath of water, into which a current of high voltage and strength is applied.
The thread is quickly wound onto a second spool and the machine thus cuts out parts that are highly accurate down to microns. This process may take 3-4 hours. Such a modernized jigsaw.
Here, too, CNC, a person only sets programs and monitors the accuracy of the operation.
From this blank
the excess is cut out so that another part can be inserted.
And I was also surprised that the thread can cut at an angle. From the middle of this cylinder a part is cut out, which is round on one side and star-shaped on the other.
Trigger details.
Here you can see that several sheets were welded together to cut out the maximum number of parts.
We leave this workshop and head to the assembly area, this is the last stage before the rifle goes to the shooting range.
These boxes contain ready-made rifles.
A specialist assembles the bolt group parts together, attaches them to the barrel, followed by the glass bedding process. A special mastic is applied to the rifle stock, metal parts are placed in it and left for a day until completely dry. Then the parts are taken out again and sent for painting, and their exact imprint remains on the stock, which allows you to match the wood to the metal. This provides greater accuracy to the weapon.
After painting, the parts are put back together. Specialists from the technical control department inspect the finished product and give a conclusion that the rifle is ready to fire.
There are also very young workers at the plant.
Every day the plant produces up to 10 rifles per day.
In addition to rifles, the plant also assembles Austrian Glock pistols of various calibers under license.
And this is a refrigerator, but you won’t find vegetables, fruits, beer, last night’s dinner or other snacks in it. It is also used when assembling the rifle. How, you ask?
The fact is that when assembling some parts, you need to screw some parts to the stock as tightly as possible. If this is done at room temperature, then the screws will cut into the product too much and can ruin it, so these parts are placed in the refrigerator for a while so that it shrinks a little (I hope everyone remembers physics) and can be screwed as tightly as needed without risk of damaging the bed.
Stages of rolling a simple barrel tube.
At the top is a blank plate for the barrel
Probably many will agree with me that the main part of a gun is the barrels. After all, they are the ones who shoot. The effectiveness of cannon shots made people want to make a small “hand” cannon. Such a cannon was found in the Tanneberg Castle in Hessen (Germany) in the middle of the last century. It was cast at the end of the 14th century. It was, of course, difficult and inconvenient to shoot from it by hand, and soon a crossbow stock was adapted to it. It turned out that in terms of shooting accuracy and accuracy, the new weapon is seriously inferior to a good bow, although in terms of energy, and therefore penetrating power, it is significantly superior to it. It quickly became clear that as the barrel length increases, the shots become more accurate. From this moment the history of firearms begins.
Today, our “breaking” hunting rifle has three main parts: the barrel (or barrels that form the barrel block), the block, and the stock.
The barrel gives direction to the flight of the shot or bullet. The more correctly and carefully it is made, the better the shot flow and the higher the accuracy.
The block locks the breech end of the barrels, serves as a connecting element between the barrels and the stock, and is the main inertial element in the weapon, absorbing recoil force. Locking, trigger and safety mechanisms are mounted in the block.
The stock provides ease of aiming the weapon at the target, natural aiming and softens the effect of recoil force due to its partial transformation into rotational moment.
Before talking about today's technology for manufacturing weapon barrels, I would like to introduce readers to a part of weapons history concerning the improvement of the manufacture of this most important part of the weapon. After all, making a good barrel is a rather difficult task even with today’s level of development of mechanical engineering. However, the perseverance, diligence and ingenuity of our distant ancestors found various options for solving this problem. Moreover, the level of quality of the best products of the 18th century seems almost mysterious to today’s specialists. We would like to tell you how the masters of the past created wonderful weapons, show some examples of them and together think about the greatness of their spirit with the hope that this will strengthen our own.
In 1811, Heinrich Anschutz (from a well-known arms dynasty) published a book about the arms factory in Suhl. He writes about four types of technologies for producing barrel tubes: regular, twisted, wound and Damascus barrels.
A regular (simple) barrel was made from a strip blank 32 inches (812.8 mm) long, 4 inches (101.6 mm) wide, 3/8 inch (9.525 mm) thick. After heating, this strip was bent using a forge on a mandrel in such a way that its longitudinal edges were butted against each other, parallel to the axis of the barrel bore. This joint was welded using the forge method and carefully forged. There are undoubted indications that both long sides of a rectangular workpiece were sometimes driven together “on a mustache” and welded not end-to-end, but overlapping. After welding and cooling, the barrels were passed through a tetrahedral reamer, the outer surface was turned on a lathe, which was then ground by hand on a large circle of soft sandstone with a diameter of 1.75 m. A screw plug was screwed into the barrel from the breech side, which was sometimes also boiled. Of course, the barrels of all muzzle-loading guns were “silenced,” regardless of the technology used to produce them.
Twisted trunk. The weld seam in a conventional barrel, located parallel to the axis of the barrel, was often the site of destruction during shooting. To avoid this, a simple welded barrel began to be reheated in the central part and twisted along the axis along the entire length so that the weld had the shape of a helix. This technique made the seam much less loaded when fired.
A wound barrel was produced by gradually winding a steel strip onto a mandrel in the form of a rod or pipe. The helical weld was successively forged with a forge hammer.
Damascus trunks. Back in the Middle Ages, swords of exceptionally high quality were made in Damascus (today Syria). As soon as the technology for their production became clear to Europeans, they tried to apply it to the manufacture of barrels. The basis of the secret was that blanks for bladed weapons were obtained by forge welding of strips of thin elements consisting of steels differing in carbon content. Initially, the welded and forged strip was folded and forged many times. Compared to conventional homogeneous blanks, Damascus had three fundamental advantages. In essence, it represented a design that combined the properties of individual materials. In addition, the composition not only eliminated internal defects that occur in a homogeneous workpiece, but also created an optimal structural orientation. Basically, Damascus trunks were produced by the winding method. However, to obtain the original strip it was necessary to do simply titanic work. First, a block of one hundred steel rods of different compositions with a square section with a side of 0.7 mm, laid in a certain order, was welded. The block had a cross-section of about 7 mm x 7 mm. This procedure required an incredibly fine blacksmith's sense, since it was easy to burn through thin wires. The welded block was heated again and rolled lengthwise. Then they took several of these twisted bars (usually three or six), welded them together and forged them into a strip. In some cases, something like braids were woven from these twists, which could consist of a different number of strands and have a different weaving pattern. The braids were welded and forged into strips. This strip was wound onto a mandrel. Then the workpiece was trimmed, the channel was passed through with a reamer, the outer surface was first turned on a lathe, then ground. The bluing process in those days consisted of treatment with fairly strong acids. As a result, low-carbon rods were etched much more strongly than high-carbon rods, and an original small pattern appeared on the surface of the barrel, reflecting the entire previous scheme for obtaining stripes. Usually on Damascus barrels the width of the stripe is visible to the naked eye.
The rapid development of metallurgy at the end of the 19th century led to the emergence of carbon steels with high mechanical properties. The prospect of using them for the manufacture of barrels seemed obvious. However, even in the first quarter of the 20th century, many European gunsmiths continued to make barrels using “Damascus technology”. Today it is necessary to understand that such barrels, although they are monuments to the fantastic zeal of gunsmiths of previous generations, are still inferior in all the most important indicators to modern alloy barrel steels. Let us remind our compatriots that steel 50A and even 50PA, from which barrels are made today both in Tula and Izhevsk, are not alloyed barrel steels. And more about Damascus trunks. A hundred or more years after manufacture, it is very likely that the forge welding of the elements may be significantly damaged and the strength of the barrels may not be sufficient to ensure shooting safety. Be very careful if you want to shoot old guns with Damascus barrels.
The introduction of chromium, vanadium, nickel, silicon, manganese and other elements into the composition of carbon steel led to a significant increase in the most important properties of barrel steels - elasticity, tensile strength, surface hardness, and corrosion resistance. Moreover, these technologies make it possible to produce steels with predetermined properties. All this made it possible to move on to the production of homogeneous blanks for rifle barrels. This process began in the last third of the 19th century and coexisted with “Damascus” technology for about half a century.
Development of technology for manufacturing rifle barrels.
The new stage begins with the abandonment of trunks obtained from strips and the transition to trunks, the channel of which was formed by deep drilling. This technology is incomparably more productive, but its implementation required solving a number of serious problems, which we would like to talk about so that modern readers can imagine the cost of obtaining guns with excellent combat. The new technology for making barrel blanks begins with forging, which not only gives the barrel blank an external shape that approximates the finished barrel, but also improves the structure of the steel by reducing its grain size. Typically, for forging, a piece of round steel with a diameter of about 50 mm is cut. The length of this blank depends on the future length of the barrel. A piece 320 mm long is enough to forge a workpiece 750 mm long with an average diameter of 30 mm. Of course, after forging, the diameter of the workpiece in the chamber area is noticeably larger than that of the muzzle. It should be noted here that during conventional forging, about 15% of the steel goes into scale. Blacksmiths say that metal “burns away.”
Gun Drill:
a - cutting plate,
b and c - guides,
d - channel for supply
coolant,
e - cavity for
chip removal
To relieve internal stresses in forged workpieces, they are heated to (approximately) 850-860 degrees and held for about half an hour. The exact heating parameters depend on the grade of barrel steel and the thickness of the workpiece. The task of relieving internal stresses is very important for all stages of barrel production. It is especially important that there are no stresses in the finished barrel tube designed to form barrel blocks from two or more barrels. The fact is that soldering with soft and especially hard solders requires significant and asymmetric heating of the barrels. The cooling of the soldered block also occurs nonuniformly. The presence of internal stresses leads to noticeable deformation of the barrels after soldering. Moreover, high heating of the inner surface of the barrels during shooting, especially intense, can cause irreversible deformation of the barrel if stress remains in it. After normalization, hardening is carried out. Its essence is to obtain optimal properties by forming a fine structure of the metal. Any steel is a phase-complex system containing at least two crystalline modifications of pure iron, iron carbide, carbides of impurity metals and solid solutions of some of these components in each other. Temperature treatment changes the phase state of this complex system and the sizes of individual phases, which very significantly affects the performance properties. Hardening consists of uniformly heating the part to a temperature depending on the composition of the steel from which it is made. Billets made of steel Sk 65, which is often used for barrels in Germany, are heated to 840 degrees. After this, it is dipped into oil at room temperature. Then the workpiece is “tempered”, for which it is heated in a muffle furnace for about 4 hours at a temperature of 580-600 degrees. Hardness, toughness, elasticity and tensile strength can be significantly influenced by such complex heat treatment.
The heat-treated workpiece is carefully straightened. This is done so that during drilling, which occurs when the workpiece rotates, it does not vibrate. The workpiece is straightened in a horizontal position while rotating, adjusting its shape with pressure rollers. After straightening, the workpiece is again subjected to heating to relieve internal stresses, then it is trimmed on both sides and chamfered.
Straightening the trunk using shadow rings
using a screw press
After this, they begin the most delicate process in making a barrel - drilling. Deep drilling, especially in a long workpiece with low longitudinal stability, is a special song. In the arms industry, special machines similar to lathes are used for this. In them, the fixed workpiece rotates, and a special drill moves forward. There are two main problems in this process: moving the drill away from the axis of the workpiece and removing chips. The first problem can be solved due to the homogeneity of the workpiece structure and the relatively low drill feed rate and cutting speed to eliminate vibration of the workpiece. Of course, these restrictions increase the drilling time. The problem of removing chips, which sometimes not only spoils the surface of the channel, but also jams the drill, is solved by special techniques. In the 19th century, “gun drills” were used; their design was close to reamers, that is, they were based on a rod, along the entire working length of which a cylindrical sector with an angle of about 100 degrees was selected. The design of the drill is quite simple and can be clearly understood from the drawing. Through a small hole in the body of the drill, a cooling emulsion is supplied to the cutting zone, which carries away the resulting chips along a groove parallel to the axis of the drill. Such machines have long become multi-spindle and fairly automated. This allows one worker to control drilling on multiple machines. This process still did not guarantee a high degree of cleanliness of the surface of the barrel bore. Chips were often the main reason for this. In addition, drilling productivity was low.
Beisner drill -
working and
back part
In 1937, Burgsmuller qualitatively changed the drilling pattern. He proposed a vertical arrangement of workpieces and a drilling direction from bottom to top for better chip removal. As the base of the drill, he used a pipe, on the working head of which three guide plates were attached and one cutting plate was welded. The cutting process occurs when cooled by compressed air, which is supplied into the gap between the surface of the drill and the walls of the resulting hole. The chips did not contact the walls of the hole at all and were carried down along with the air. The significantly greater moment of resistance to torsion that the “pipe” had compared to the profiled rod allows, in addition to obtaining good surfaces, to use higher cutting and feed speeds when drilling.
In 1942, Beisner improved this method. He returned the drilling machine to a horizontal position, suggested using oil as a coolant, and improved the drilling head. Oil was supplied under pressure into the gap between the drill and the resulting cylindrical surface and carried the chips through the central channel into a special collection box. The surface was very smooth, to some extent due to polishing with guides. However, after drilling, the bore is processed with a reamer.
Before starting to process the outer surface of the barrel, it is straightened: the straightness of the channel axis is checked and, if necessary, straightened using a screw press. The correctness of the channel is checked using shadow rings, which every hunter can do himself. But the straightening process requires not only good vision, but also a great sense of metal, which comes only with experience. The fact is that the trunk has elasticity. Therefore, if it straightens under load, then after it is removed it will partially return to its original state. An experienced craftsman feels how much the barrel needs to be “bent” so that after removing the load it becomes perfectly correct.
Grooving necks for steady rests:
1 - center, 2 - sliding sleeve,
3 - stand, 4 - neck for steady rest
After shaping the barrel bore, another difficult task arises: turning the outside of the barrel. The main difficulty is to ensure that the center of the outer surface coincides exactly with the center of the bore. If this is not done, the receiver tube will turn out to have different walls. In addition, due to the large ratio of the length of the barrel to its diameter, when turning the surface of the barrel, it must be fixed with two steady rests, for each of which the necks must first be turned. To correctly perform this operation, a special coupling is installed in the middle of the barrel length, which allows you to correctly hold the barrel by its untreated surface when turning necks for steady rests. When the journals are machined, the coupling can be removed and the external turning of the barrel can be carried out according to the pattern. These turnings may cause some deformation of the barrel. Therefore, the trunk is once again monitored by shadow rings and, if necessary, straightened. Finish turning and grinding is carried out after the necks for the steady rests are sanded separately. The final stage of making barrel tubes is fine grinding, called honing in the gunsmithing industry.
Rotary forging scheme:
1 - heating with high frequency currents,
2 - beginning of forging, 3 - forging process,
4 - end of forging
A significant advance in the manufacture of gun barrels is their mandrel forging. Of course, the equipment for this process is not cheap. Therefore, molding barrels by forging is cost-effective only for large production volumes. However, the savings in money and time are also significant. When making barrels using the hot rotational forging method, blanks with a length of 260-280 mm and a diameter of about 35 mm are used. In it, a through hole with a diameter of 20.5 mm is made using a Beisner drill. The workpiece is fixed on a hardened, carefully polished mandrel, shaped like the inner surface of the finished barrel. After electric induction heating of the workpiece to the required temperature, it is fed into the forging zone, where it, rotating along its axis, passes under the blows of cross-shaped hammers. In one and a half minutes, the workpiece takes the external and internal shape of the barrel with the chamber. Hardening is not carried out after such forging. The external shape of the barrel is finished by turning and grinding. The bore is roughed out using a reamer. The final processing of the barrel bore, including the chamber and choke, is carried out after assembling the barrel block.
An even more advanced method of making barrels is cold forging on a mandrel. One of its advantages is that it saves about 15% of expensive barrel steel that goes into scale during hot forging. In addition, the inner surface of the barrel is an exact copy of the mandrel, so you can get completely finished barrels (with chamber, choke and rifling). The surface of the bore only requires polishing. In addition, the structure of the cold-forged barrel provides it with high mechanical properties. True, cold forging requires more powerful hammers and longer duration. It lasts just over three minutes. The external shape is completed by turning and polishing. The correctness of the channel axis is checked after this technology and, if necessary, it is straightened. The final stage of manufacturing individual barrel blanks is shooting and branding.
Vladimir Tikhomirov
Master gun 10-2004
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