Admittedly the most important component of a rifle, the barrel delivers the projectile to where you are aiming. A really good one does it with extreme precision and consistently repeats the process again and again. Hammer forging is a process which can produce extremely accurate barrels..
Barrels- we expect a lot from them but often give little thought to the manufacturing process. Most people are familiar with how cut-rifled barrels are made. A hole is drilled at bore diameter (the size that the lands will measure across at their highest point- for the .308 Winchester, that would be 0.300”), and a cutter is pulled through to create the grooves that will have a diameter equal to the bullet meant for the caliber (0.308” for the same cartridge). The cutter is twisted as it is pulled, to create a specific rate of twist (like 1 turn in 12”). What is left in the barrel is the rifling, also known as the lands. The metal for the lands was always there- it is the grooves that are created in the cut rifling process.
Another commonly used method is button rifling. A hole is first drilled at near bore diameter. The rifling is formed by pulling (while twisting) a hardened steel button (more like a pea or bean-like shape) through the bore, which has the shape of the grooves and lands formed into its surface. A button looks much like a short section of a firedbullet. The metal for the grooves is displaced, the land material displaces somewhat, and you now have a rifled barrel.
The last increasingly popular method for making rifled barrels is called hammer forging. It may conjure up visions of a massive blacksmith’s anvil, a large hammer and a machinist with arms and a chest like Arnold Schwarzenegger! How is it really done? Fortunately, I was able to arrange a visit to Arnold’s home country of Austria, where the hammer forging process was invented. A two-day visit to Steyr Mannlicher was planned. They were chosen for several reasons.
Steyr Mannlicher
Located in the town of Steyr (first established around 900 AD), Steyr Mannlicher has been making firearms since the mid-1800s. Presently, they manufacture the world-famous AUG military rifle in use by thirty-four countries, the SSG sniper bolt action rifle used by military and police forces, the M-Series pistols, the famous and original Scout rifle, and two series of hunting rifles. The Classic Mannlicher line has fine wood...
stocks, including the traditional full stock model. The ProHunter series includes popular US chamberings in blued or stainless versions. Additionally, a full range of metric calibers is offered.
The Classic Mannlicher line has fine wood stocks, including the traditional full stock model.
Steyr has been using the hammer forging process for almost fifty years, having long since perfected it. The forging equipment is made by GFM, also located in Steyr. GFM pretty much has the world market for hammer forging machines used to make gun barrels. Steyr Mannlicher rifles have since always borne the traditional, distinctive hammer forged, twisted exterior finish. I have been able to work with many of their rifles as I own more of them than I probably should.
Consistently, I am amazed at how well they shoot, and how easily they clean. If there is a place to learn about the hammer forging process, surely Steyr is a good place to go. They have never before allowed a writer into their facility to see in such detail how they perform hammer forging. I am grateful that Steyr was willing to open their doors, and I am certain that you will enjoy reading about the process.
The Hammer Forging Process-
- Raw Material
The raw material for chrome moly or stainless barrels comes in as round stock 1.3” in diameter and about 12-feet long. During the forging process, the barrels will grow about30% in length. Because of this growth, the raw stock is actually cut to lengths that are much shorter than the finished barrel size. When making pistol barrels, Steyr cuts a piece of blank that will actually yield six barrels. The entire blank goes through the hammer forging process and then is cut up to yield the many pistol barrels.
- Deep Hole Drilling and Honing
The first true machining process is where the blank is deep hole drilled. Using specially designed equipment and very long drill bits, the raw blank gets the initial hole drilled all the way through. A pressure lubrication system keeps the chips flushed out of the hole during the process. When hammer forging, the starting hole needs to be larger than the finished groove size. For a .308 barrel, forging requires starting with a hole .315” in diameter.
The goal of deep hole drilling is to get a starting point for...
all following operations. It does not leave a “nice” finish- at this early stage it does not need to. Honing is the next step for the blank. Special machines (very tall ones at that) secure the blanks in an upright position and processes them two blanks at a time. Honing is a three-step process- coarse, medium and fine. Up to now, the blanks really do not look like much more than a fat piece of steel round stock with a small hole through it. The next step transforms it into something a shooter could at least imagine to be a barrel.
CNC Rough Contour Turning
Computer Numerically Controlled (CNC) machines are wonderful pieces of machinery. Using the “x, y & z” coordinates (length, width and depth), lathes, or mills can be programmed to digitally reproduce parts by the thousands… all alike in every dimension. The “chunky” blank of 1.3” diameter next gets sent to a CNC lathe. Here, the blank gets rough turned down to a configuration that we could identify as a rifle barrel. The general contour is familiar, but the breech end gets a little step that will be used to properly secure it during the hammer forging phase. The CNC machining for the rough contour takes but a few minutes, and precedes the actual forging process.
Terms and Tools of Forging
Before we get into the actual process, some basic terminology first needs to be covered. The machine that forms the barrels' outside shape, while also creating the internal rifling, is called a cold hammer forge. The machine Steyr chose for this process is manufactured by GFM, right in the town of Steyr. GFM is a world leader in forging machines that are used throughout many industries, including automotive, aviation, and medical. The cold hammer forges that Steyr use cost over one million dollars each.
The machine that forms the barrel outside shape, while also creating the internal rifling, is called a cold hammer forge.
The tool that goes inside the barrel to create the grooves and lands, is called a mandrel. It is made of special hardened tool steel, and looks very much like a steel cigarette, with twisting grooves running the length. Note that a mandrel has a reverse image of what you see when you look down a barrel. In a barrel, the lands stand out; on a mandrel they are stepped in. A mandrel looks like...
what you would get if you poured metal into the barrel, and then pulled it out. The mandrel is mounted on the end of a rod which is inserted into the barrel, called the mandrel rod. The machinist also informally referred to the mandrel as a“
mouse… because it goes into the hole”.
The palm-sized metal blocks that impact the barrel are appropriately called hammers and are used in sets of four. They are made of a vitrified hard metal that is shaped by being electrically eroded. The area that impacts the barrel consists of two flattened surfaces, shallow-angled like two adjacent sides of a STOP sign (but sixteen-sided). A lead-in section allows a gradual transition to the final contour. The two flats on each hammer give the outside of the Steyr forged barrels their distinctive spiral pattern. Different barrel contours require different sets of hammers.
Forging Details
About one-dozen contoured blanks are loaded into a rack on the forge. The START button is pressed, and the automation process begins. A pair of mechanical “hands” grabs the first blank and presents it to the starting position. An automatic chuck grabs the small step of the breech/ chamber end. As the assembly begins to turn, the barrel is fed into position just before the hammers. At the same time, the mandrel rod is advanced in to its working position, centered between the four hammers. The mandrel will always stay centered under the hammers throughout the forging process. The hammers begin to impact the barrel in unison while the mandrel rotates inside of the barrel at the same rotational speed of the barrel. Rate of twist is controlled by the twist of the lands machined into each mandrel.
Rate of twist is controlled by the twist of the lands machined into each mandrel.
The hammers all strike the barrel at the same moment, each with a force of over 100 tons, at over 1,000 strikes per minute. The hammers do not have to travel far, but obviously, very fast and very hard. During this process, the blank is cooled and lubricated with a water/oil solution. The rotating barrel blank is fed into the hammers at a rate of about five inches per minute. The actual forging process takes about four to five minutes, resulting in around 16,000 individual impacts.
It was not overly noisy to stand right next to the equipment while a...
blank was being forged. While I stood next to the operator, we could converse at only a slightly elevated speaking level. As a safety measure, the machinist regularly wears hearing protection. I thought that I would feel severe vibration during the forging. What I
found instead was each opposing pair of hammers canceled out each other, resulting in minimum disturbance.
As stated earlier, the blanks grow in length during the forging process up to 30% or more. As the barrel forging is progressing, the barrel passes through the hammer impact area and emerges fully formed from the off side. When the process is fully complete, another pair of mechanical hands grabs the barrel and deposits it onto a completion tray. A barrel, so deposited, can be immediately picked up with bare hands. The water/oil lubrication system leaves it cool to the touch.
Understandably, the cold forging process induces great stress into the barrel. As such, the next step is to stress relieve the barrels in a controlled environment. To accomplish this, the barrels are heated to almost 600 F for about four hours. After this process, the barrels are faced at both ends, chambered, and threaded for the action..
As Steyr is ISO 9001 certified, constant quality control checks were evident throughout the process. When I got to see where the interiors of the barrels were inspected, I was impressed with how uniformly perfect the rifling grooves and lands were through the full-length. I had come to expect a factory mirror finish in Steyr forged barrels. To see the same surface magnified and just as flawless was a treat. In fact, as the optical magnifier traveled down the inside of the barrel, it almost looked like a still image because the rifling was as perfect and consistent as could possibly be imagined.
After inspecting four or five barrels and seeing virtually nothing at all in the way of imperfections, I asked the barrel maker what a “bad” barrel looked like inside? He paused for a moment and then went to the corner of the shop where he found an old, rejected barrel. Placing it on the inspection bench, he inserted the optical probe and began his search. Apparently, he knew where to look. After just a moment, he pronounced, “There… look at this!” All I saw was a tiny dark spot- a void- perhaps the size the period at the end of this sentence. He seemed disgusted that such a horrible defect had been found in one of his barrels. He obviously...
takes great pride in what he does.
Benefits for the Shooters
The cold hammer forging process compresses metal in to create the rifling, improving the solidity and hardness of the material. The smooth interior is also less prone to
fouling and cleans up very easily. Another result is a dramatically extended accuracy life of the barrel. For example, the military AUG barrel (often used in the full-auto mode) has a recommended service life of up to twenty-two thousand rounds.
What can a hunter expect from a Steyr hunting rifle in regards to accuracy? I once ran a test to work up a series of progressive, reduced loads, to help my 12-year old daughter learn how to shoot. For the test, I grabbed my 20” barreled ProHunter in .260 Remington, Accurate 5744 powder (great for reduced loads), and Hornady 95-grain V-Max bullets. I proceeded to load three rounds each with 5744, in two-grain increments, from 21 to 29 grains. Placing five targets up at 100 yards, I fired the charges left to right, without stopping. The results? Velocities went from around 2,200 fps to 2,900 fps as the charge was increased. Accuracy? The largest group was 5/8”… the smallest measured .287”!
Extensive tests were also performed with the .376 Steyr in a ProHunter shortly after it was introduced. The cartridge beats out the .35 Whelen or .350 Remington Magnum and even approaches the .375 H&H, with less powder and recoil. I now have loads for eleven different bullets (in a wide weight range) that average three-shot groups of one-inch or less at 100 yards. The best loads consistently shoot into less than 1/2″! This rifle, and a Scout in .308, went with me to Zimbabwe, helping to collect over two-dozen head of game..
The best loads consistently shoot into less than 1/2″! This rifle, and a Scout in .308, went with me to Zimbabwe
At the factory, a 9.3×62 ProHunter, which had not yet been shot for accuracy, was scoped and given to me to test fire. Using factory ammo (slightly exceeding .35 Whelen performance), I placed five shots into less than one inch… at 100 meters. So far, I have worked with Steyrs in a half-dozen calibers and have always been pleased to be able to work up great loads… with a minimum of fuss. I have yet to test one that would not shoot one-half inch, 3-shot groups with my handloads.
While the hammer forging...
process is an interesting story, serious hunters and shooters will most certainly be impressed with the confidence the end result can give them on the range, or especially, when hunting in the field.