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 from Sunnen Products Co. 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.
In 2015 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 … a new manufactured machine with the changes we wanted on it and [subsequently] ordered a second one.”
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.
Sunnen states that: “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. 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.”
Computer-Controlled Bore-Honing
Honing can be done with great precision through the use of advanced, computer-controlled honing machines. Sunnen Products Company offers an advanced 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 employs more than 600 people worldwide.
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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 from Sunnen Products Co. 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.
In 2015 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 … a new manufactured machine with the changes we wanted on it and [subsequently] ordered a second one.”
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.
Sunnen states that: “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. 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.”
Computer-Controlled Bore-Honing
Honing can be done with great precision through the use of advanced, computer-controlled honing machines. Sunnen Products Company offers an advanced 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 employs more than 600 people worldwide.
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This article was originally written by noted rimfire gunsmith Bill Myers. Sadly, Bill passed away in May 2010, but his legacy lives on. He pioneered many advancements in rimfire gunsmithing and Myers-built guns still win matches in benchrest competition.
Crafting competitive rimfire benchrest rifles is considered an art as much as a science. The smith must understand subtle, yet critical aspects of vibration control, barrel tuning, and rifle balance. In the United States, only a handful of gunsmiths consistently turn out rimfire BR rifles that consistently run at the front of the pack at major matches. Bill Myers was one of those master craftsmen. In this article Bill discussed the process of building a winning rimfire BR rig. He reveals some interesting secrets, including his procedures for testing bedding performance and his barrel indexing system. Bill’s methods obviously work, as the Suhl-actioned rifle featured here won a truckload of trophies in its very first match.
Building a Match-Winning Rimfire Benchrest Rig
by Bill Myers
In my opinion, a winning rimfire benchrest rifle is probably twice as difficult to build as a competitive centerfire rifle. The relatively slow .22 LR bullets stay in the barrel much longer than centerfire bullets. This means that vibration control is critical. Likewise bedding is critical. Bore finish and lapping are very important. The amount of bore taper or “choke” can have a huge effect on accuracy. Ignition is also very important and above all, rimfire BR rifles need a very stable stock that tracks perfectly. A rimfire that shoots great is a complete marriage of all components and of the shooter’s need to be aware of everything possible.
Click Photo to Zoom
The rifle featured in this article was built from scratch with attention to all the details that go into accuracy. The goal was to build a gun that could win from the get-go. This would be a “Spec Gun”, meaning a rifle that was personally tested and tuned by me for optimum performance before it went out to the customer.
The Suhl trigger is as good as it gets so no change was needed. It easily adjusts down to about 2 ounces.
Baer Stock in Bubinga Wood
There are many choices when you start to build a complete rifle. It has to shoot well and it has to catch ones eye, or it’s just another rifle on the line. I prefer wood stocks on rimfires for two reasons: they are very stable if the right wood is used and they have a certain traditional appeal to many shooters. I chose Bubinga wood for this particular gun because it is very stable and heavy, it has a very dense grain and a very pronounced figure with a natural red color. The Bubinga is a very forgiving wood to work with.
Gerry and Bruce Baer in Pennsylvania do all my stock blanks. I do all my own inletting and bedding. The blank weighed 4.5 pounds when it came off of Bruce Baer’s duplicator. This Bubinga wood is so hard that it did not need pillars, but I put them in anyway. I bed all my stocks with Loctite Steel Bed liquid and add filler to desired thickness. The final bedding is done with an aircraft tooling epoxy that does not deteriorate over time. The stock has an ebony butt plate and six (6) coats of automotive clear, polished to a “high buff” finish.
Suhl 150-1 Action Accurized and BN-Nickel Plated
I used a new, unfired Suhl 150-1 action. As explained in the sidebar below, the Suhl 150 actions were originally crafted in East Germany for position rifles. They have a very fast lock-time and come with an outstanding trigger. However, they need some work when adapted to a modern BR gun. The action needed to be accurized and threaded. I have a special tool that I use to accurize actions. It uses two sets of spiders for dialing-in the bolt raceway. After the bolt raceway is running true, one can thread and true up all bearing surfaces so that everything is in perfect alignment with the action raceway bore.
BN-Nitride Plating on Action
I decided to plate the action and all bolt parts with Boron Nitride nickel plating. I bough the BN Electroless Nickel Kit from Caswell Plating and did the job myself. I started by bead-blasting the action so that it would end up with a “satin” finish. The plating material is then applied in a tank. The Boron Nitride goes directly into the plating solution, but you need to use a pump to keep the solution agitated so the BN distributes evenly.
Once the action is completely ready (the metal must be perfectly prepped, with no contaminants), the process goes easily and can be completed in about half an hour. The end result is a very slick, low-friction finish, that is .0002″ (two ten-thousandths) thick and hard as glass. The Boron Nitride makes everything very smooth. After the plating job, the action was noticeably slicker than before.
The cone breech (photo below) permits the barrel to be INDEXED (rotated around bore axis) to any position on the clockface. You then test various rotation settings to find the best accuracy. The system does work. Some barrels shoot best in a particular rotational setting. E.g. with index mark at 3 O’clock vs. 12 O’clock.
Fitting and Chambering the Barrel
As for a barrel, I had two good choices: one Shilen 1:16″-twist, 4-groove ratchet and one Benchmark 1:16″-twist, 3-groove. Both barrels were very accurate and at the end, I decided to leave the Shilen on the rifle because I wanted to put the Benchmark on another Suhl I’ve set aside for myself. I chambered the barrel for Eley flat nose EPS. We’ve found the gun also shoots the new Lapua X-ACT ammo very well.
The barrel finished at 25″ long and features a tuner by the Harrell brothers of Salem, Virginia. I use a flat 90° crown–it’s the most accurate and its gives a good seal against the tuner. I also use a 45°, 12-flute cutter that leaves no burr when cutting the crown. This chamfer protects the crown when cleaning the barrel. There is no sharp edge for the brush or jag to hit on the return stroke. The barrel was headspaced at .043″ and I use a tapered reamer ground by Dave Kiff of Pacific Tool & Gauge in Oregon. The chamber leade area is lightly polished to remove reamer burrs. The breech end of the barrel is machined with a 1/2″ ball end mill to produce what I call a “Myers cone breech.” Technically, it has a sloping radius as you can see, rather than a straight-sided cone. Finishing the breech in this fashion facilitates indexing the barrel, as the barrel can be rotated to any position (on the clockface), without requiring new extractor cuts.
Barrel Indexing — Finding the “Sweet Spot”
When indexing a barrel, one rotates it to different clockface positions relative to the action. Imagine marking a barrel at TDC or 12 o’clock, and then rotating it so the mark is at 3 O’clock, 6 )’clock, 9 O’clock and so on. At each position one shoots groups to determine at which index setting best accuracy is achieved.*
I know that barrel indexing is controversial. I don’t want to get into a lengthy debate other than to say that I believe that careful and thorough testing can reveal a “preferred” index position for a good barrel. With the barrel set in that particular position relative to the action I believe the barrel can yield optimal performance.
I perform the indexing tests indoors at 50 yards. I use a rail-gun with floating action. The barrel is held in place with a clamping fixture similar to an Anschutz 2000-series action. Basically, two vertically-stacked metal blocks clamp around the barrel. I can index the barrel this way simply by unclamping the barrel blocks, rotating the barrel and then re-clamping the system. I have a special system so the action can stay in the same position, even as the barrel is rotated.
It takes time and effort to get solid indexing results. Normally I shoot at least 400 rounds of ammo in 3-4 indexing sessions. Shooting a handful of groups is not enough. You may think you’ve identified the best index position, but you need to shoot many more rounds to verify that. Also, in a very good barrel, the effects of indexing may be subtle, so it will take many groups to confirm the optimal position. In my experience, really good “hummer” barrels do not benefit as much from indexing as an “average” barrel.
Accuracy Testing with Both Barrels
I tested the rifle indoors at 50 yards at the Piney Hill Benchrest Club range. There was no finish on the stock, but it shot well in my one-piece rest with the Benchmark 16-twist, 3-groove barrel and no added weight on the tuner. I shot 30 rounds of Eley Match EPS Black Box (1064 fps) and had 25 Xs and five 10s on the IR 50/50 style target. Not too shabby for a new barrel with no special break-in.
When the Shilen barrel arrived, I installed it on the rifle. By this time the stock had been clear-coated and finished, and the action had been polished and plated. I shot the Shilen barrel outside since it was too hot in the building. The first target was a 250-19X with a new lot of Eley Match EPS Black Box (1054 fps). The gun shot well. My friend Tony Blosser asked to shoot the gun, and he drilled a 250-20X in a steady wind using the same Eley ammo. See target at right.
Advanced Procedures — Vibration Control and Tuner Position
Barrel Tuning Using 2-Way Electronic Indicators
Before competing with this rifle, I put it in a firing fixture I use to tune the barrel. I employ a pair of very expensive Swiss 2-way electronic min/max hold indicators. These measure both up movement and down movement of the barrel as the gun is fired. I can measure the actual vertical travel of the barrel at any position from the front of the receiver to the tuner. I can also tell how long the barrel vibrates, time-wise. Using this fixture I found that the Shilen barrel was very consistent in readings and seemed to work well with no additional weight on the tuner. No barrel ever stops vibrating completely — but this was close, showing less than .002″ of total movement.
Bedding and Vibration Control
I have found that measuring the actual movement of the barrel during firing tells me a lot about the quality of the bedding. I have learned that if I see very big movements (e.g. .010″ up and .005″ down), then there may be a problem with the bedding. I saw this kind of big swing on a rifle with bedding that had not cured properly.
Another pattern I watch for is uneven vertical movement. For example, if the barrel vibrates .008″ up but only .002″ down, that tells me the bedding has issues. As noted above, I look for minimal vibration travel (after the tuner is fitted and optimized), and I also want that travel to be relatively equal both up and down. Good rimfire gunsmiths agree that proper bedding has an important influence on vibration control and tuning. By measuring actual barrel movement during firing, we can, to an extent, quantify how well the bedding is working. At a minimum, we can see if there’s a serious bedding problem.
Trial by Fire — Shooting the Gun in Competition
After semi-gluing in the action, the rifle was shooting great. So, I decided to take it to the Maryland State Unlimited Championship to see if it was truly competitive — whether it could “run with the big dogs”. As it turns out, the Bubinga Suhl was more than just competitive. The rifle won three of the six cards and won the meters championship. In the photo below you can see all the trophies the gun won in its very first match. One of the other competitors in Maryland, dazzled (and perhaps a bit daunted) by the Bubinga Suhl’s stellar performance, told me: “Sell that gun Bill. Whatever you do, just get that darn rifle out of here.” Confident that this was a rifle capable of winning major matches, I packed up the rifle and shipped it to Dan Killough in Texas. Killough has shot some impressive scores with the gun.
Suhl Target Rifles — East Germany’s Legacy
Suhl 150 rifles were manufactured in former East Germany (GDR) by the Haenel firearms factory in the town of Suhl. This region has a long history in arms production. In 1751, Sauer & Sohn founded the first German arms factory in Suhl. Following WWII, Suhl 150s were produced for Communist Bloc marksmen, including East German Olympic shooters. Prior to German unification, the East German national shooting arena was located at Suhl and hosted many top-level competitions including the 1986 ISSF World Championships.
Superb Rifles with Amazing Triggers
As a product of East Germany, the “mission” of the Suhl 150 was to rival the accuracy of the Anschütz, Walther and other premium match rifles built in the West. East German shooting teams wanted to finish on top of the podium, so they needed a rifle with superb inherent accuracy. The Suhl 150s have an outstanding trigger that can be adjusted down to about two ounces. The Suhl 150 action, like the Anschütz 54, boasts an extremely fast lock-time — an important factor in a position rifle. And Suhl barrels were legendary for accuracy.
Suhl 150 Benchrest Conversions
Many of the first used Suhl 150s that made it to America were converted to Benchrest rifles because the action/trigger/barrel combination was unbeatable for the price. Some of the barrels on these “surplus” Suhls were phenomenal — as good as any custom barrels available today. It was not unknown for a Suhl 150 barreled action, transplanted into a benchrest-style stock, to win BR matches with the original barrel. Today, however, most of the Suhl benchrest conversions end up with modern, American-made barrels. While some older Suhl barrels can “shoot with the best of ‘em”, new barrel designs optimized for use with tuners have an edge, at least in benchrest circles. That’s why builders such as Bill Myers swapped out the Suhl barrel with something like a Benchmark reverse-taper two-groove.
Today Suhl 150 rifles are very hard to find in North America. In 2006, a used Suhl 150, even without sights, might fetch $1200.00 or more. Then, in 2007 through early 2008, hundreds of Suhl match rifles were imported. This drove prices down, and those “in the know” snapped up complete Suhl 150s at prices ranging from $450 to $850 (see 2007 advert at right), depending on condition.
Many of these rifles were left “as built” and used successfully in prone competition. Others were converted into benchrest and silhouette rifles, “parted out” for the actions and triggers. If you were able to grab one of those imports at a good price–consider yourself lucky.
* Bill Myers actually created his own clamping rimfire action to facilitate barrel indexing. CLICK HERE for Myers Rimfire Action. To index the barrel, Myers simply loosened three clamping-bolts and rotated the barrel in the action. Because there is no thread to pull the barrel in or out, the headspace stays the same no matter how much the barrel is rotated. With a threaded action, you might have to use shims to test different rotational positions, or otherwise re-set the shoulder with each change.
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Precision rifle shooters don’t have to hit a big-league fastball, or launch a top-fuel dragster in the blink of an eye. Nonetheless, reaction times are important in our sport — both for competitive shooters and hunters. Want to catch that prairie dog before he slips down his hole? You’ll need to be quick. Want to win at short-range benchrest? Then you’ll need to watch your windflags and respond quickly to a change. Miss a major wind-shift and you could ruin your whole weekend.
Here’s a fun test of reaction times from HumanBenchmark.com. The way it works is that, after clicking “Start”, you wait until the background color changes from red to green. The instant you see green, immediately click your mouse. The average (median) reaction time is 215 milliseconds. Hint: If you keep your finger “preloaded” in contact with your mouse button you can shave some milliseconds — but don’t “jump the gun”.
Tips for Faster Times
Here are three tips to speed up your reaction times:
1) Respond to the color change (by itself), rather than wait to read the word “CLICK!” after the box shifts to green.
2) Try focusing at the corner of the box, rather than the center. This may help you react “without thinking”.
3) Have your index finger “poised and ready” over the left button–you can shave milliseconds by very slightly depressing the button before you actually click.
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Cabelas.com has just made available some of the hard-to-find Hodgdon propellants, in 1-lb containers. H4831sc, Benchmark, H380, Hybrid 100V, Retumbo, H414 are all showing as “in stock” with prices ranging from $22.99 to $27.99 per pound, with a $20.00 HazMat fee. There is a catch — purchasers are limited to two (2) pounds of any Hodgdon powder product per order, per day. The 1-lb containers of H4831sc are currently on sale at $25.99, marked down from $27.99. NOTE: Varget was available earlier today at Cabelas.com, but Varget actually sold out minutes before this story was published. Good luck grabbing some of the other powders!
Accurized and BN-Nickel Plated
BN-Nitride Plating on Action
Fitting and Chambering the Barrel
Accuracy Testing with Both Barrels
Today Suhl 150 rifles are very hard to find in North America. In 2006, a used Suhl 150, even without sights, might fetch $1200.00 or more. Then, in 2007 through early 2008, hundreds of Suhl match rifles were imported. This drove prices down, and those “in the know” snapped up complete Suhl 150s at prices ranging from $450 to $850 (see 2007 advert at right), depending on condition.
