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December 26th, 2018

The Cut-Rifling Process — A Short History and Demonstration

Pratt & Whitney Cut rifling hydraulic machine

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.

Kolbe Border Barrels Firearms ID

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.

Pratt & Whitney Cut rifling hydraulic machine

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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May 8th, 2016

Sunnen Barrel Honing System Used by Pac-Nor Barreling

Pac-Nor PacNor Barreling honing hone Sunnen lapping barrel
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.”

Pac-Nor PacNor Barreling honing hone Sunnen lapping barrel
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 PacNor Barreling honing hone Sunnen lapping barrel
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.”

Pac-Nor PacNor Barreling honing hone Sunnen lapping barrel

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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March 10th, 2016

Barrel-Making Methods Explained in Walther Video

Lothar Walther barrelsAt 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.”

Credit The Firearm Blog for this informative interview.
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February 6th, 2016

Barrel-Making: How Ruger Crafts Hammer-Forged Barrels

Ruger Firearms Barrel Making Hammer Forging
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.

Ruger Firearms Barrel Making Hammer Forging
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.

Ruger Firearms Barrel Making Hammer Forging
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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February 24th, 2015

Tech Trends: Precision Barrel Bore-Honing

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!):

Barrel Bore honing cut-rifled rifling hammer forging accurateshooter.com

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.

Barrel Bore honing cut-rifled rifling hammer forging accurateshooter.com

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.

Barrel Bore honing cut-rifled rifling hammer forging accurateshooter.com

Barrel Bore honing cut-rifled rifling hammer forging accurateshooter.com

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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March 3rd, 2014

Krieger Barrels — Like Father, Like Sons

Krieger Barrels John KriegerKrieger 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.

Krieger Barrel-Making Processes Shown in Video
00:24 – Cryogenic treatment of steel blanks
00:38 – Pre-contour Barrels on CNC lathe
01:14 – Drilling Barrels
01:28 – Finish Turning on CNC lathe
01:40 – Reaming
01:50 – Cut Rifling
02:12 – Hand Lapping
02:25 – Cut Rifling
02:40 – Finish Lapping
02:55 – Outside Contour Inspection
03:10 – Engraving
03:22 – Polish
03:50 – Fluting
03:56 – Chambering
04:16 – Final Inspection

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June 2nd, 2011

Lothar Walther’s Woodall Explains Barrel-Making Methods

Lothar Walther barrelsAt 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.”

Credit The Firearm Blog for this informative interview.
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