Gun-maker Bear Creek Arsenal has a good article on its website about rifling barrels. The article explains four common methods of rifling the interior of barrels: Cut Rifling, Broach Rifling, Button Rifling, and Hammer Forging. In addition, the article describes a new (and somewhat radical) method, Cation Rifling, which employs acid to etch rifling. READ Full Article.
The main focus of the article is on Cold Hammer Forging of barrels. This requires massive, expensive tooling, but the results can be very consistent. Many top gun-makers, such as FN, HK, and Ruger, have used the hammer forging process. And now Bear Creek Arsenal also offers hammer-forged barrels. Bear Creek recently acquired two state-of-the-art cold hammer forging machines. With hammer forging, a chamber can be formed and barrel contour shaped at the same time. This process produces some of the most consistent barrels available today. Here is a summary of how Cold Hammer Forging works:
Cold Hammer Forging — Machinery and Process
A cold hammer-forged barrel starts life… as a short and fat blank with a polished hole running through the center. A hardened mandrel of proper width (caliber) and rifling pattern — again reversed/inverted — is placed into the smooth bore. The pair go into a forging machine that compresses the steel against the mandrel, hammering it into final shape. The barely detectable external spiral patterns that remain on some barrels are imprints from those hammers at work. Some companies polish them out, however.
Cold hammer forging machinery is very expensive, representing a significant investment for companies. However, when the hammer forging process is done and the mandrel removed, the resulting barrel is the proper length and profile with rifling that is consistent and butter smooth. No lapping is required — a time and expense saver — although a stress-relief step often follows.
The process takes place at room temperature, despite the misleading “cold” terminology. There is a hot hammer forging process, but the equipment is even more expensive and the slight improvement in grain consistency hasn’t proven advantageous enough for a return on that investment. Performance is impressive and consistent.
One of the biggest advantages of a cold hammer forged barrel is longevity. They… survive abuse and last longer. The manufacturing process adds those enviable virtues with each strike of those hammers — strengthening the metal in a work-hardening process employed by blacksmiths for centuries.
Comparing Popular Rifling Methods
What rifling process should you choose? If long-distance is your passion and you home brew custom cartridges to print tiny groups in the next zip code, cut rifling is the optimum choice. Button rifling is a solid second choice, but not always the Holy Grail long-distance shooters dream about. Cold hammer forged barrels, however, last longer and [offer great performance for the price.]
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Gun-maker Bear Creek Arsenal has a good article on its website about rifling barrels. The article explains four common methods of rifling the interior of barrels: Cut Rifling, Broach Rifling, Button Rifling, and Hammer Forging. In addition, the article describes a new (and somewhat radical) method, Cation Rifling, which employs acid to etch rifling. READ Full Article.
The main focus of the article is on Cold Hammer Forging of barrels. This requires massive, expensive tooling, but the results can be very consistent. Many top gun-makers, such as FN, HK, and Ruger, have used the hammer forging process. And now Bear Creek Arsenal also offers hammer-forged barrels. Bear Creek recently acquired two state-of-the-art cold hammer forging machines. With hammer forging, a chamber can be formed and barrel contour shaped at the same time. This process produces some of the most consistent barrels available today. Here is a summary of how Cold Hammer Forging works:
Cold Hammer Forging — Machinery and Process
A cold hammer-forged barrel starts life… as a short and fat blank with a polished hole running through the center. A hardened mandrel of proper width (caliber) and rifling pattern — again reversed/inverted — is placed into the smooth bore. The pair go into a forging machine that compresses the steel against the mandrel, hammering it into final shape. The barely detectable external spiral patterns that remain on some barrels are imprints from those hammers at work. Some companies polish them out, however.
Cold hammer forging machinery is very expensive, representing a significant investment for companies. However, when the hammer forging process is done and the mandrel removed, the resulting barrel is the proper length and profile with rifling that is consistent and butter smooth. No lapping is required — a time and expense saver — although a stress-relief step often follows.
The process takes place at room temperature, despite the misleading “cold” terminology. There is a hot hammer forging process, but the equipment is even more expensive and the slight improvement in grain consistency hasn’t proven advantageous enough for a return on that investment. Performance is impressive and consistent.
One of the biggest advantages of a cold hammer forged barrel is longevity. They… survive abuse and last longer. The manufacturing process adds those enviable virtues with each strike of those hammers — strengthening the metal in a work-hardening process employed by blacksmiths for centuries.
Comparing Popular Rifling Methods
What rifling process should you choose? If long-distance is your passion and you home brew custom cartridges to print tiny groups in the next zip code, cut rifling is the optimum choice. Button rifling is a solid second choice, but not always the Holy Grail long-distance shooters dream about. Cold hammer forged barrels, however, last longer and [offer great performance for the price.]
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The question of barrel break-in is controversial. Some folks advocate an elaborate, lengthy cycle of shooting and brushing, repeated many times — one shot and clean, two shots and clean and so on. This, it is argued, helps barrels foul less and shoot more accurately. Others say minimal break-in, with patching and brushing after 10-15 rounds, is all you need. Still others contend that break-in procedures are a total waste of time and ammo — you should just load and shoot, and clean as you would normally.
We doubt if there will ever be real agreement among shooters concerning barrel break-in procedures. And one must remember that the appropriate break-in procedure might be quite different for a factory barrel vs. a custom hand-lapped barrel. This Editor has found that his very best custom barrels shot great right from the start, with no special break-in, other than wet patches at 5, 10, and 15 rounds. That said, I’ve seen some factory barrels that seemed to benefit from more elaborate break-in rituals.
What’s the best barrel break-in procedure? Eric Mayer of Varminter.com decided to ask the experts. Eric interviewed representatives of three leading barrel manufacturers: Krieger, Lothar-Walther, and Shilen. He recorded their responses on this video. In order of appearance, the three experts are:
Shilen, Krieger, and Walther Experts Talk about Barrel Break-in
Do I Need to Break-In a New Rifle Barrel?
Eric Mayer of Varminter.com says: “That is a simple question, [but it] does not necessarily have a simple answer. Instead of me repeating my own beliefs, and practices, on breaking-in a new rifle barrel, I decided to answer this one a bit differently. While we were at the 2016 SHOT Show, we tracked down three of the biggest, and most popular, custom barrel makers in the world, and asked them what they recommend to anyone buying their barrels, and why they recommend those procedures. We asked the question, and let the camera run!” Launch the video above to hear the answers — some of which may surprise you.
Barrel Break-in — Initial Inspection and Cleaning
This video explains that you should always inspect and clean the bore of your barrel before sending rounds through it. There may be remnants of the production process, such as lapping residues, that you’ll want to get out of the bore. We’ve even seen a few tiny metal pieces in some factory barrels. And it’s always wise to borescope a new barrel to see if there are visible defects in the rifling such as lands that have flawed edges — we’ve seen that on some cheaper barrels.
Barrel Break-In — Ian Klemm’s Surprising Observations
Here’s a 10-minute Vortex Nation interview with Ian Klemm. Ian, a 4-Time F-TR National Champion is one of America’s best long-range shooters. In this video, Ian explains his approach to barrel break-in, which may surprise you. Does barrel break-in even matter? Conventional wisdom says “Yes” and perhaps there’s some truth to that, but Ian argues that break-in is NOT nearly as important as the internet wants you to believe. Ian believes that you don’t need to waste a ton of time/ammo to get your barrel ready to shoot extremely accurately. This may be particularly true with premium hand-lapped custom barrels.
Barrel Break-In Procedures with Keith Glasscock
Keith Glasscock is also one of America’s greatest F-Class shooters who has finished second at the Nationals multiple times. Keith is also a highly-respected wind coach who has a popular YouTube video channel, Winning in the Wind. In this video, Keith explains his procedure for breaking-in his match barrels. He starts by bore-scoping the barrel and cleaning it. If he finds some burrs he may use some JB Bore Paste, a patch, and a worn brush and “give that throat a little scrub” (See 1:30 time-mark). He used different stroke lengths to avoid putting a “step” in the throat. When he’s satisfied he goes to the range. He fires the first five rounds, then cleans. He then fires quite a few rounds before cleaning the barrel again and beginning load development (See 8:25 time-mark).
General Barrel Break-in Procedures Recommended by Brownells
Brownells Gun Techs Steve Ostrem and Caleb Savant tackle a thorny topic: breaking in a new barrel. What IS breaking-in a barrel? And WHY do it? The rifling of a freshly machined barrel has microscopic burrs and sharp edges. “Breaking-in” is the process of putting bullets down the bore to smooth out those rough spots. The goal is to round down the sharp edges so they’re not stripping copper off a bullet as it travels the bore, which leads to fouling that leads to reduced accuracy and inconsistent groups. In a very minor way, you’re actually lapping the barrel. The breaking-in process works best on cut-rifled and button-rifled barrels. Cold hammer-forged, chrome-lined, or nitrided barrels — such as commonly found on AR-15s — may not benefit much from the process. Pistol barrels really don’t need to be broken in because larger-diameter bullets are not so much affected by tiny variations in the bore. Likewise, break-in is more helpful for a .17, .20, or .22 caliber rifle than a .45 caliber rifle.
George Gardner of G.A. Precision Talks About Barrel Break-In
G.A. Precision’s George Gardner is a leading figure in the PRS/NRL world. In this video, George makes the valid point that not all barrels require the same amount of break-in. George says some barrels require very little break-in, while others benefit from a more elaborate break-in process that helps reduce future copper and powder fouling. He calls this “seasoning” the barrel so it fouls less. For a typical barrel, George’s recommended process (4:25 time-mark) starts with one shot, then clean for three one-round cycles. This is followed by three shots then clean, with repeat 3-shot cycles if need. For cleaning George prefers nylon brushes (5:50 time-mark). NOTE: George also makes a very important point — you MUST swab the chamber and get it dry between cleaning cycles (5:30 time-mark).
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Gun-maker Bear Creek Arsenal has a good article on its website about rifling barrels. The article explains four common methods of rifling the interior of barrels: Cut Rifling, Broach Rifling, Button Rifling, and Hammer Forging. In addition, the article describes a new (and somewhat radical) method, Cation Rifling, which employs acid to etch rifling. READ Full Article.
The main focus of the article is on Cold Hammer Forging of barrels. This requires massive, expensive tooling, but the results can be very consistent. Many top gun-makers, such as FN, HK, and Ruger, have used the hammer forging process. And now Bear Creek Arsenal also offers hammer-forged barrels. Bear Creek recently acquired two state-of-the-art cold hammer forging machines. With hammer forging, a chamber can be formed and barrel contour shaped at the same time. This process produces some of the most consistent barrels available today. Here is a summary of how Cold Hammer Forging works:
Cold Hammer Forging — Machinery and Process
A cold hammer-forged barrel starts life… as a short and fat blank with a polished hole running through the center. A hardened mandrel of proper width (caliber) and rifling pattern — again reversed/inverted — is placed into the smooth bore. The pair go into a forging machine that compresses the steel against the mandrel, hammering it into final shape. The barely detectable external spiral patterns that remain on some barrels are imprints from those hammers at work. Some companies polish them out, however.
Cold hammer forging machinery is very expensive, representing a significant investment for companies. However, when the hammer forging process is done and the mandrel removed, the resulting barrel is the proper length and profile with rifling that is consistent and butter smooth. No lapping is required — a time and expense saver — although a stress-relief step often follows.
The process takes place at room temperature, despite the misleading “cold” terminology. There is a hot hammer forging process, but the equipment is even more expensive and the slight improvement in grain consistency hasn’t proven advantageous enough for a return on that investment. Performance is impressive and consistent.
One of the biggest advantages of a cold hammer forged barrel is longevity. They… survive abuse and last longer. The manufacturing process adds those enviable virtues with each strike of those hammers — strengthening the metal in a work-hardening process employed by blacksmiths for centuries.
Comparing Popular Rifling Methods
What rifling process should you choose? If long-distance is your passion and you home brew custom cartridges to print tiny groups in the next zip code, cut rifling is the optimum choice. Button rifling is a solid second choice, but not always the Holy Grail long-distance shooters dream about. Cold hammer forged barrels, however, last longer and [offer great performance for the price.]
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You’ve probably heard of cut-rifling, but did you know this process was invented in Germany nearly 500 years ago? Read on to learn more about how a cut-rifled barrel is made…
The cut-rifling process, used by leading barrel-makers such as Bartlein, Border, Brux, Krieger, and Obermeyer, can yield a very high-quality barrel with a long useful life. Cut-rifled barrels have been at the top in short- and long-range benchrest competition in recent years, and cut-rifled barrels have long been popular with F-Class and High Power shooters.
You may be surprised to learn that cut-rifling is probably the oldest method of rifling a barrel. Invented in Nuremberg around 1520, the cut-rifling technique creates spiral grooves in the barrel by removing steel using some form of cutter. In its traditional form, cut rifling may be described as a single-point cutting system using a “hook” cutter. The cutter rests in the cutter box, a hardened steel cylinder made so it will just fit the reamed barrel blank and which also contains the cutter raising mechanism.
Above is a computer animation of an older style, sine-bar cut-rifling machine. Some machine features have been simplified for the purposes of illustration, but the basic operation is correctly shown. No, the cut-rifling machines at Krieger don’t use a hand-crank, but the mechanical process shown in this video is very similar to the way cut-rifling is done with more modern machines.
Read About Cut-Rifling Process at Border-Barrels.com
To learn more about the barrel-making process, and cut-rifling in particular, visit FirearmsID.com. There you’ll find a “must-read” article by Dr. Geoffrey Kolbe: The Making of a Rifled Barrel. This article describes in detail how barrels are crafted, using both cut-rifling and button-rifling methods. Kolbe (past owner of Border Barrels) covers all the important processes: steel selection, hole drilling, hole reaming, and rifling (by various means). You’ll find a very extensive discussion of how rifling machines work. Here’s a short sample:
“At the start of World War Two, Pratt & Whitney developed a new, ‘B’ series of hydraulically-powered rifling machines, which were in fact two machines on the same bed. They weighed in at three tons and required the concrete floors now generally seen in workshops by this time. About two thousand were built to satisfy the new demand for rifle barrels, but many were broken up after the war or sold to emerging third world countries building up their own arms industry.
Very few of these hydraulic machines subsequently became available on the surplus market and now it is these machines which are sought after and used by barrel makers like John Krieger and ‘Boots’ Obermeyer. In fact, there are probably less of the ‘B’ series hydraulic riflers around today than of the older ‘Sine Bar’ universal riflers.
The techniques of cut rifling have not stood still since the end of the war though. Largely due to the efforts of Boots Obermeyer the design, manufacture and maintenance of the hook cutter and the cutter box have been refined and developed so that barrels of superb accuracy have come from his shop. Cut rifled barrel makers like John Krieger (Krieger Barrels), Mark Chanlyn (Rocky Mountain Rifle Works) and Cliff Labounty (Labounty Precision Reboring)… learned much of their art from Boots Obermeyer, as did I.” — Geoffrey Kolbe
Video find by Boyd Allen. Archive photos from Border-Barrels.com. In June 2013, Birmingham Gunmakers Ltd. acquired Border Barrels. Dr. Geoffrey Kolbe has set up a new company called BBT Ltd. which produces chamber reamers and other gunsmithing tools and gauges. (Thanks to L. Holland for the Kolbe update).
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Pac-Nor Production Manager Casey Dichter says the Sunnen hone produces a consistency in bore diameter that is much superior to hand-lapping. The Sunnen machine has all but eliminated the standard pre-rifling lap. “You can really tell the difference between a bore that was honed before rifling and one that was [only] lapped”, notes Dichter.
Gun Barrel Honing System Hits Target for Pac-Nor Barreling
Manufacturing precision rifle barrels has always been something of an art that involves hand lapping of the bore surface twice, before and after the rifling profile is cut or swaged in by a rifling button. In fact, a bright, hand-lapped bore is considered one of the hallmarks of a precision rifle barrel, despite the inherent variations from manual work done by people who get bored and tired from the monotonous chore. Pac-Nor Barreling, Inc. set its sights on this issue more than a year ago and hit the X-ring with the newly developed Sunnen HTE honing machine. The machine has all but eliminated Pac-Nor’s pre-rifling lap, which is the more difficult and time-consuming of the two laps. Pac-Nor is also producing as many custom barrels as ever, but with a slightly smaller staff. “Our objectives with the hone were to build a better product with less labor, and the honing machine has exceeded my expectations,” said Pac-Nor Production Manager Casey Dichter. “The hone produces a consistency in bore diameter that is head and shoulders above lapping, within two to three millionths of an inch end-to-end when it’s really dialed in,” he said. “This, in turn, improves the consistency of the rifling process by minimizing variation in the depth of the grooves. We still finish lap after rifling, but it’s easier because we just polish off the fine crosshatch finish that may be left after honing and rifling.”
The Sunnen hone secures the barrel blank in a 3-jaw chuck, with honing oil pumped into one end while the tool works from the opposite end. Sunnen’s specialized Long Bore Tool uses metal-bond diamond or CBN superabrasives to quickly remove reamer marks, waviness, tight spots and other imperfections left by upstream processes.
Honing is an ideal replacement for hand lapping barrel blanks before rifling. It quickly removes reamer scratches and surface waviness without labor-intensive hand lapping. A typical 600-grit abrasive can produce a 6-10 microinch Ra (0.15 to 0.25 µm) finish in a reamed barrel blank. By producing a consistent bore diameter (±0.0001″ or less), parallelism, roundness and surface finish end to end, honing yields more consistent performance from rifling buttons and cutters, resulting in a constant groove depth. The ideal bore geometry reduces distortion of the bullet shape.
Pac-Nor’s barrel-making process starts with cutting and facing premium bar stock, followed by gun drilling, done by four Pratt & Whitney twin-spindle machines and an Eldorado CNC twin spindle. After reaming, the barrels are gauged for size. Depending on the condition of the reamer, 0.0004″ to 0.0007″ of material is left in the bore. This must be manually lapped out or honed out to final size for rifling. “Everyone who works here has done hand-lapping,” said Dichter. “It’s an unpleasant job, particularly if the reamer is starting to get dull. Lapping may take 10 to 45 minutes, depending on the caliber of the barrel. We tried to shorten this, but when chatter marks get ‘ironed’ into the surface by the rifling button, the finish lap is even longer and more difficult, so there is no advantage. With lapping, too, there is potential for variation, simply because it’s a manual process. Lapping can also be a production limiter and in our region we have a very small labor force to draw on when we want to grow.”
Pac-Nor cuts and faces premium bar stock, then gun drills on one of five twin-spindle machines, followed by reaming of the blanks. This rack of barrel blanks awaits completion.
The company had explored honing in the nineties, but re-visited the idea when Sunnen introduced its HTE honing machine in 2014. The HTE is a horizontal machine that can hone small-bore rifle barrels, with a diameter range of 0.150″ to 0.790” (4-20 mm), and lengths up to 60″ (1,524 mm). Designed specifically for long small bores, the machine features an extremely sensitive drive and tool feed system that provide maximum protection against tool overload/breakage. Tool specific force limits and run settings are stored in the touch-screen PC control, allowing the system to sense tight sections in the bore and correct them automatically.
Sunnen also developed a new Long-Bore Tool (LBT) designed to take on industry’s most difficult honing challenges in small bores of .17 caliber rifle barrels. The tool quickly remove reamer marks, waviness, tight spots and other imperfections left by upstream processes. The LBT utilizes metal-bond diamond or CBN super-abrasives for high productivity, long life and fast cycle times. Precision-machined of through-hardened tool steel, the LBT can produce bore accuracies of 0.000027″ (0.0006 mm) for diameter, roundness, and taper – from first part to last.
“We are currently honing about 80 percent of what we make and will do more as we acquire the tools in different calibers,” said Dichter. “Although there is a trade-off in cycle time and abrasive cost for additional honing, we are still able to run our reamers two to three times longer than when we lapped alone. With a hand lap, the time and effort increase when the reamer is getting dull.”
After honing, each barrel is inspected again before rifling with a pull-button. Pac-Nor makes its own Accu-Twist carbide rifling buttons and can provide different rifling styles, including polygonal, per the customer’s choice. A button is attached to a rod and the rod is pulled through the barrel. The company’s hydraulic rifling machine utilizes a CNC-machined twist bar with a helix angle that matches the twist rate requested by the customer. The final twist rate is confirmed afterward using a Barrel-Scan electro-optical twist measurement system.
The barrel is then stress-relieved in a tempering furnace, followed by contouring of the outer shape and final, finish lapping of the bore. “During the finish lap, you can really tell the difference between a bore that was honed before rifling and one that was lapped,” said Dichter. “You can easily sense any remaining tight or loose spots in the bore. The diameter uniformity and roundness of the honed bore are superb. The lap also feels different in a honed bore.”
In competitive shooting where winning scores may be separated by thousandths of an inch, a few millionths of an inch improvement in the uniformity of a Pac-Nor barrel may make a big difference for a skilled shooter. For more information, visit www.sunnen.com or contact:
Sunnen Products Company
Mr. Bob Davis
Global Communications Mgr.
Sunnen Products Company
Tel: 314-781-2100
bdavis [at] sunnen.com
About Pac-Nor Barreling Inc.
Pac-Nor Barreling is a true custom manufacturer catering to bolt-action rifle shooters. The company’s principle markets are law enforcement, military, competitive shooters and hunters. Started in 1984 by avid shooter and company President Chris Dichter, Pac-Nor is now in its second generation under his son, Casey. In addition to barrel manufacturing, the shop will install the barrel on a customer’s action, or add features such as muzzle brakes or fluting on bolts and barrels etc.
The shop runs two shifts per day. A day shift of ten people produces 30-40 custom barrels of different calibers in 416R stainless or chrome-moly steel. A night shift of three people produces one type of barrel — about 50 AR-15 barrels per day for a rifle OEM.
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At the IWA Trade Show in Germany a few years ago, a correspondent for The Firearm Blog interviewed Woody Woodall, who runs Lothar Walther’s USA operation. While many shooters assume that Walther hammer-forges most of its barrels like some other European barrel-makers, in fact Lothar Walther USA uses the button rifling technique for most of its US-made barrels.
In the video below, created for The Firearm Blog, Woodall explains that button rifling involves some extra steps to ensure a good result: “The extra work that goes into it is that you’ve got to make rifling, stress relieve it, and have it come out the right size. And it takes a lot of skill to do that. Lothar Walther invented button rifling in 1925, if a better way of making rifling came out, we’d be glad to go to it.”
Woodall explains that hammer forging is a good method for mass production, but it is costly to set up: “Hammer forging is relatively new, it came out in 1934, but did not come into prominence until the 1950s…. But the cost of [hammer forging] in the world today is getting above what the market will bear for barrels. [Hammer forging] is more complicated. As the hammers hit the barrel the barrel gets longer, but the hammers have to hit uniformly so the barrel [stays] straight. There’s a higher failure rate in that. There’s also some surface delamination that can occur, and some other issues. So if you’re hammer forging, you really have to pay attention to the details. So, it’s like button rifling, only ten times more complicated. It’s for super-high-volume production… The large companies tend to use the hammer forging, intermediate size companies tend to use the buttoning, and craft companies tend to use the cut rifling. All three [methods] can make an equally accurate barrel.”
This image shows a barrel in the process of hammer forging. Watch this operation starting at 1:15 in the video linked below.
You have probably heard the term “hammer-forged barrel”. But do you know how the cold hammer-forging process works? In this interesting video from Ruger, you can see the full barrel making process, including cold hammer-forging on a massive machine. Watch long rods of steel barrel material get cut to length, then drilled. After that Ruger uses CNC machines to contour the barrels before hammer forging.
Anyone with an interest in barrel-making should watch this video:
As the barrel is cold hammer-forged, a giant machine literally pounds the barrel from all sides around an internal carbide mandrel, which forms the rifling inside the bore. The actual hammer-forging is illustrated starting at 1:15 in this video. Through the process of cold-working the barrel around the mandrel, the barrel ends up with a longer length, a smaller outside diameter, and a higher hardness.
Before hammer forging, the barrels are deep-hole drilled, four at a time, with a bit that is slightly larger diameter than the caliber planned for the barrel.
Following the drilling, the barrel rod is placed in CNC machines to be turned down to the correct outside shape and size and both ends are trimmed.
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Some custom barrel makers are now honing barrels (after drilling) to improve bore diameter uniformity, smooth the interior finish, and reduce barrel lapping times. For years, large-scale manufacturers of hammer-forged barrels have employed honing. Now the process is being used by smaller, “boutique” barrel-makers. This article explains how and why barrel honing is done. Take the time to watch the video. For anyone with an interest in barrel-making, this video is an eye-opener…
Barrel Honing Process Demonstrated (Worth Watching!):
For custom barrel makers, honing is a time-saver and cost cutter. A few minutes on a honing machine can cut lapping times in half, leaving a cross-hatched surface finish in single or low double-digit Ra. Honing is the same process used to make diesel fuel injectors with bore roundness and straightness controlled to fractions of a micron (<0.000040"), with surface finish Ra ≤0.15 µm (6 µin).
A key manufacturing process used for hammer-forged barrels is now getting attention from the makers of custom button-rifled barrels. This process is precision bore-honing. Honing produces a high-quality bore surface fast, which is critical to hammer forging. (Why is honing so important with hammer forging? Surface finish is the one feature of the barrel that cannot be controlled in hammer forging. Surface imperfections in a barrel blank tend to be amplified as the blank is formed on the rifling mandrel. And if the bore is chromed afterwards, imperfections in the surface finish become even more obvious.)
Honing dramatically improves bore diameter size uniformity and accuracy, surface finish and roundness throughout the length of the barrel. It can certainly be used in place of a pre-rifling lap. The chief difference between a lapped and honed bore is the direction of the finish lines in the bore. Honing leaves fine spiraling crosshatch lines, while a lap leaves lines going longitudinally in the bore. After rifling the manufacturer can remove the crosshatch finish with a quick lap if desired. Honing is fast, accurate, and can be automated. Its surface quality and geometry can duplicate lapping, except for the longitudinal lines of the lapped finish.
Frank Green of Bartlein Barrels told us: “We worked with Sunnen and we did all the initial testing on the prototype machine for them. The machine works great! We ordered and received last year a new manufactured machine with the changes we wanted on it and we just ordered a second one a month or so ago. Should be here next month.”
Computer-Controlled Bore-Honing
Honing can be done with great precision through the use of advanced, computer-controlled honing machines. Sunnen Products Company recently introduced a new machine for .17 to .50-caliber barrels (see control panel below). The spindles on this machine can correct bore size imperfections so small only an air gauge can measure them. The consistency this allows improves bore uniformity, which, in turn, produces more accurate barrels for the precision market.
Sunnen Products Company is the world’s largest vertically-integrated manufacturer of honing systems, tooling, abrasives, coolants and gauging for precision bore-sizing and finishing. Sunnen’s customers include manufacturers of diesel and gas engines, aerospace components, hydraulic components, oil field equipment, and gun/cannon barrels. Sunnen, which just celebrated its 90th anniversary, employs more than 600 people worldwide.
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Krieger Barrels Inc. is a family-run business. Founder John Krieger now works with two of his sons in the business, Andrew (“Andy”) and Mark. At SHOT Show 2014 we had a chance to chat with John and Andy. John told us that he is very proud to work with his two sons. He said that Andy, who has a degree in engineering, brings an important skill set and a new level of scientific expertise to the business. On his part, Andy says that his father is a “great boss… and the best teacher you could have”. Meet this father and son barrel-making team in this short video.
John Krieger and Andrew Krieger
How does Krieger Barrels produce such a great product year in and year out? It takes a lot of highly-skilled labor and some serious machinery to produce outstanding cut-rifled barrels. To illustrate the barrel-making process, Krieger has produced a fascinating video, filmed at Krieger’s production facility in Richfield, Wisconsin. This video shows the process of single-point, cut-rifled barrel-making start to finish. If you love big, powerful machines, you’ll enjoy this video. Its really quite amazing to see all that’s involved in the production of cut-rifled barrels.
How Krieger Barrels Are Made (MUST-WATCH video — one of the best we’ve ever featured).
For anyone interested in accurate rifles, this is absolutely a “must-watch” video. Watch blanks being cryogenically treated, then drilled and lathe-turned. Next comes the big stuff — the massive rifling machines that single-point-cut the rifling in a precise, time-consuming process. Following that you can see barrels being contoured, polished, and inspected (with air gauge and bore-scope). There is even a sequence showing chambers being cut.
Here is a time-line of the important barrel-making processes shown in the video. You may want to use the “Pause” button, or repeat some segments to get a better look at particular operations. The numbers on the left represent playback minutes and seconds.
At the IWA Trade Show in Germany earlier this year, a correspondent for The Firearm Blog interviewed Woody Woodall, who runs Lothar Walther’s USA operation. While many shooters assume that Walther hammer-forges most of its barrels like some other European barrel-makers, in fact Lothar Walther USA uses the button rifling technique for most of its US-made barrels.
In the video below, created for The Firearm Blog, Woodall explains that button rifling involves some extra steps to ensure a good result: “The extra work that goes into it is that you’ve got to make rifling, stress relieve it, and have it come out the right size. And it takes a lot of skill to do that. Lothar Walther invented button rifling in 1925, if a better way of making rifling came out, we’d be glad to go to it.”
Woodall explains that hammer forging is a good method for mass production, but it is costly to set up: “Hammer forging is relatively new, it came out in 1934, but did not come into prominence until the 1950s…. But the cost of [hammer forging] in the world today is getting above what the market will bear for barrels. [Hammer forging] is more complicated. As the hammers hit the barrel the barrel gets longer, but the hammers have to hit uniformly so the barrel [stays] straight. There’s a higher failure rate in that. There’s also some surface delamination that can occur, and some other issues. So if you’re hammer forging, you really have to pay attention to the details. So, it’s like button rifling, only ten times more complicated. It’s for super-high-volume production… The large companies tend to use the hammer forging, intermediate size companies tend to use the buttoning, and craft companies tend to use the cut rifling. All three [methods] can make an equally accurate barrel.”
We doubt if there will ever be real agreement among shooters concerning barrel break-in procedures. And one must remember that the appropriate break-in procedure might be quite different for a factory barrel vs. a custom hand-lapped barrel. This Editor has found that his very best custom barrels shot great right from the start, with no special break-in, other than wet patches at 5, 10, and 15 rounds. That said, I’ve seen some factory barrels that seemed to benefit from more elaborate break-in rituals.
At the 
