How to flute a rifle barrel

Fluting a Bartlein barrel reduces weight and adds a custom appearance to your custom rifle

A Bartlein barrel with 10- 3/16" flutes coated in graphite black Cerakote.

The controversy of fluted barrels

Fluting a rifle barrel is somewhat controversial.  Shooters, barrel makers and gunsmiths all seem to have different views on what fluting accomplishes, how well it works, whether or not it is detrimental to accuracy and if it is even necessary.  Chances are, the answer to your fluting questions will change depending on who you ask.

Does fluting a barrel save weight?

Yes, cutting flutes in a barrel saves weight.  Fluting a rifle barrel provides the shooter a more rigid barrel at a given weight.  For instance, a heavier 5.5 pound fluted barrel will be more rigid when compared to a non fluted barrel of 5.5 pounds with a lighter contour.  This is beneficial to shooters looking to shave weight for field use, or trying to cut weight for a competitive class.  On a heavy barrel, fluting can remove 8-12 ounces; with sporter contours, fluting can remove 4-6 ounces.  As the barrel contour decreases, the weight savings does as well.

Does fluting a barrel increase rigidity?

Fluting does not increase the rigidity of a barrel.  In the case of two barrels of the same contour, the fluted barrel will not be more rigid then the non fluted barrel.

Does fluting a barrel decrease accuracy?

Barrel makers are divided on whether or not fluting is good or bad for accuracy.  Some barrel makers flute barrels, some do not.  The concern is whether or not the fluting process adds stress to the barrel.  For instance, this link to Lilja Barrels shows they do not think it does, while this link to Shilen Barrels shows they think it is a bad idea.

Karl Feldkamp of Kampfeld Customs, well known for his bolt and barrel fluting, claims that he has only had one barrel become less accurate from the fluting process over the years.  You can read about his experiences here. (Side note, if you don’t plan on fluting your own barrel and would like the work performed, I would recommend Karl).

Obviously, if you flute your own barrel, like I do for this article, your warranty will be void with the barrel maker.

Do fluted barrels cool quicker?

Yes, they do. What is interesting is the mechanism that facilitates this cooling is part of the debate.  Some engineers, smiths and barrel makers feel that the increased surface area provided by the flutes increases the rate at which the barrel cools.  Others feel that the decreased mass has a great effect on the rate of cooling then the increased surface area.  The theory being the decreased mass of the fluted barrel retains less heat and therefore cools at a more rapid rate.

Do fluted barrels look cool?

Yes, they do.  If nothing else the fluted barrel adds a unique custom touch to your project.

Getting started with fluting

Fluting is a machinery dependent operation.  To flute a barrel, you will need a milling machine with a capacity that’s large enough to handle your barrel.  For a rifle barrel, this most likely means you’ll need access to a full size knee-mill like the Bridgeport that I’ll be using for this article.  Horizontal mills can also be used with great success.

You’ll also need a way to index (rotate and align) the barrel.  For most shops, this would normally mean some sort of super-spacer, rotary table, or indexing head and tail-stock assembly.  For this article I’ll be using a rotary table with chuck and a tail stock.

You can cut flutes with a convex rotary cutter, like the PTG I’ll use here, or with a ball-nosed endmill.  The advantage of the convex cutter is it will cut faster, deeper and have a nice transition into and out of the barrel. Ball-nosed endmills are typically more common in most smaller shops and cost less.  Using a ball-nosed endmill comes at the price of decreased speed and depth of cut.  On a vertical milling machine, the ball-nosed endmill will mean that the cut has to be made from the top down.  This will require the barrel to have additional support underneath.

A 3/16" PTG fluting cutter (left) and solid carbide ball-nosed endmill (right).  Both will do the job, but the PTG cutter will cut faster and deeper.

A 3/16″ PTG fluting cutter (left) and solid carbide ball-nosed endmill (right). Both will do the job, but the PTG cutter will cut faster and deeper.

The PTG cutter has 10 thick carbide teeth.

The PTG cutter has 10 thick carbide teeth.

Parts for the barrel fluting project

I ordered the following items from Brownells for this project:

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Time to get fluting

I am working on a barrel that has been chambered in the 223 Ackley Improved.  The barrel is a Bartlein with a Heavy Varmint contour.  This contour is quite heavy with a straight, 5.000″ long shank at the chamber end.

I decided to cut ten .090″ deep flutes.  Different barrel makers have different guidance for how deep to flute (if to cut them at all).  As a general guideline, they normally suggest staying a minimum of .150″ to .200″ away from the bore. Since this barrel has a .224″ bore diameter, and is 1.000″ at the muzzle, I could have cut my flutes a little bit deeper. If you haven’t fluted a barrel before, make sure you verify your depth of cut with the manufacturer before cutting a flute that ends up being too deep, potentially compromising the structural integrity of the barrel.

Prior to making the cuts on my barrel, I made a series of test runs on a scrap barrel given to me by a benchrest shooter.  He had an old fire cracked stainless barrel that allowed me to experiment with the RPM of the cutter and the feed rate of the X-axis power feed on my milling machine.  Benchrest shooters change barrels the way most of us change stocks. Many of them hold onto their shot out barrels and are willing to part with them for a good cause.

Since my Bartlein barrel has already been chambered and installed on a rifle, I needed to make sure it will be properly indexed when the fluting is completed.  I scribed a witness mark at top dead center on the barrel while it was still in the action prior to removing it.  You will see how I use this to align the barrel in the fixture below.

I am using a 10" rotary table equipped with a 3-jaw chuck to index the barrel.

I am using a 10″ rotary table, equipped with a 3-jaw chuck to index the barrel.

An adjustable tail-stock is placed at muzzle end of the barrel.

An adjustable tail-stock is placed at the muzzle end of the barrel.

Since I do not want the barrel tenon's shoulder to get damaged by the chuck's jaws, I put an old recoil lug on the tenon to protect it.  Note the black mark with the scribed line.  This witness mark denotes top center of the barrel.

Since I do not want the barrel tenon’s shoulder to get damaged by the chuck’s jaws, I put an old recoil lug on the tenon to protect it. Note the black mark with the scribed line. This witness mark denotes top center of the barrel.

I start by aligning the taper of the barrel parallel to the milling machine.  I use a .001" dial indicator on a long magnetic base to zero in the barrel.  Note the large angel plate behind the barrel.  This is essential to eliminating chatter and providing a rigid set up for cutting the flutes.

I start by aligning the taper of the barrel parallel to the milling machine. I use a .001″ dial indicator on a long magnetic base to zero in the barrel. Note the large angle plate behind the barrel. This is essential to eliminating chatter and providing a rigid set up for cutting the flutes.

I zero the dial indicator at one end of the barrel, slide the table over to the other end of the taper and see how much the difference is.  I then shift the rotary table slightly to align the barrel.  I continue this until the barrel is within .001" over the length of the taper.

I zero the dial indicator at one end of the barrel, slide the table over to the other end of the taper and see how much the difference is. I then shift the rotary table slightly to align the barrel. I continue this until the barrel is within .001″ over the length of the taper.

Since the barrel has already been installed, I want to index the a "rib" in between the flutes up.  I use a .0001" indicator to determine the side of the barrel.

Since the barrel has previously been installed, I want to index a rib in between the flutes so that it’s pointing up. I use a .0001″ indicator to determine the center of the barrel. The indicator will be at its highest point when it passes over the center of the barrel.

I then align the top center witness mark I made earlier.  I have the rotary table set to 18 degrees.  Since I am making ten flutes, each will be 36 degrees apart.  Placing the top at 18 degrees will put the rib in the center of two flutes.

I then align the top center witness mark I made earlier. I have the rotary table set to 18 degrees. Since I am making ten flutes, each will be 36 degrees apart. Placing the top at 18 degrees will put the rib in the center of two flutes.  At this point I also secured the angle plate behind the barrel (not shown).  This is critical to provide a smooth cut without chatter.

To align  the cutter I use a an endmill to mark the center of the barrel.  With marker on the barrel, I run a straight end mill into the barrel until it makes a mark.

To align the cutter I use a an endmill to mark the center of the barrel. With marker on the barrel, I run a straight endmill into the barrel until it makes a small mark.

I install the fluting cutter in the mill.  Using a piece of thin plastic stock (a cut off piece of an inexpensive ruler) I will raise and lower the Z-axis of the mill until it is perpendicular.  I can then verify the cutter is aligned by comparing the witness mark I cut earlier with the path of the cutting tool.

I install the fluting cutter in the mill. Using a piece of thin plastic stock (a cut off piece of an inexpensive ruler). I raise and lower the Z-axis of the mill until it is perpendicular. I can then verify the cutter is aligned by comparing the witness mark I cut earlier with the path of the cutting tool.

With everything set, I plunge the cutter into the barrel and start cutting the flute.

With everything set, I plunge the cutter into the barrel and start cutting the flute.  I am only cutting along the taper.  I start about 1″ from the beginning of the taper and end about 2″ from the end of the barrel.  I set my digital read out (DRO) at 0.0000 at the end of the cut so I would know when to slow down and stop each flute.

Close up of the first cut.  I ran my cutter at 550 RPM and 4.24 inches per minute.  I had a fire cracked barrel to practice feed rates on.

Close up of the first cut. I ran my cutter .090″ deep at 550 RPM and ~4.25 inches per minute.

I cut my flutes .090″ deep in one pass.  I had made some practice cuts on a scrap barrel at a variety of RPMs, feed rates and depth of cuts and was happiest with the results from this.

I didn't use any coolant and managed to keep both the cutter and work piece cool to the touch.  If you spent time figuring out the correct feeds for your tooling and material, you will be pleased with the results.  When the cutter reaches the end of the flute, I stop the mill, and back the cutter off.

I didn’t use any coolant and managed to keep both the cutter and work piece cool to the touch. If you spend time figuring out the correct feeds for your tooling and material, you will be pleased with the results. When the cutter reaches the end of the flute, I stop the mill, and back the cutter off.

Here is my cheat sheet to remind me of the rotary table settings for each of the ten flutes.  I am cutting the flutes opposite one and other, 180 degrees apart- sorta like tightening the bolts on a car tire.  From the discussions I have had with various smiths, I am unsure this is a necessary precaution.

Here is my cheat sheet to remind me of the rotary table settings for each of the ten flutes. I am cutting the flutes opposite each other, 180 degrees apart- sorta like tightening the bolts on a car tire. From the discussions I have had with various smiths, I am unsure this is a necessary precaution. Some do it, some don’t.

For each cut, the rotary table is unlocked, rotated, and locked.  The flute is then cut.

For each cut, the rotary table is unlocked, rotated, and locked. The flute is then cut.

Here is the barrel with all ten flutes cut and removed from the milling machine.  The edges of the flutes sharp, with a slight burr I will sand off.  I am also going to recut the crown since I had the tail stock's dead center pressed against it.

Here is the barrel with all ten flutes cut and removed from the milling machine. The edges of the flutes are sharp and have a slight burr, which I will sand off. I am also going to recut the crown since I had the tail stock’s dead center pressed against it.

Since I had the tail stock dead center against the crown, I dialed the barrel in on my lathe and re-crowned it.  No sense in taking any chances after all of that work.

I dialed the barrel in on my lathe and re-crowned it. No sense in taking any chances after all of that work.

I mount the barrel in a barrel spinner so I can deburr it.

I mount the barrel in a barrel spinner so I can deburr it.

I'll be using a rubber wheel with an abrasive belt on my buffer to deburr the barrel.

I’ll be using a rubber wheel with an abrasive belt on my buffer to deburr the barrel.

The combination of barrel spinner and buffer makes short work of removing any burrs from the barrel.

The combination of barrel spinner and buffer makes short work of removing any burrs from the barrel. 80 grit abrasive cloth is used to clean off the inside edges.

The barreled action is reassembled, degreased, blasted with aluminum oxide and then coated with graphite black Cerakote.

A Bartlein barrel with 10- 3/16" flutes coated in graphite black Cerakote.

A Bartlein barrel with 10- 3/16″ flutes coated in graphite black Cerakote.

Close up view of the flutes.

Close up view of the flutes.

Top view of the flutes.

Top view of the flutes.

I headed off to the range to see how it shot. I don’t think fluting hurt the accuracy of this barrel?

I would say this rifle shoots well even when fire forming.  This was my best 5-shot group of the day, .352".  69 SMK on top of Reloader 15 in a Lapua case. 100 yards, 20F with 25MPH no value gusts.

I would say fluting didn’t hurt this barrel! This was my best 5-shot, 100- yard group of the day, .352″. 69 SMK on top of Reloader 15 in a Lapua case. 100 yards, 20F with 25MPH no value gusts.

8 Flute barrel

While I had the rotary table and tail stock on the mill I decided to flute a short 308 barrel I had.  This barrel has 8- 3/16″ flutes.

Here is the set up I used to flute a 16.75" 308 Winchester barrel.  The barrel is a stainless Shilen #7 select match.  I left the brake on the end to protect the crown from damage, the tailstock didn't even mark the brake.

Here is the set up I used to flute a 16.75″ 308 Winchester barrel. The barrel is a stainless Shilen #7 select match. I left the brake on the end to protect the crown from damage, the tailstock didn’t even mark the brake.

I ran eight 3/16" flutes, .090" deep.

I ran eight 3/16″ flutes, .090″ deep.

The barrel prior to deburring and finishing operations as it came off the milling machine.  I think I like the 10 fliute barrel better then this one.

The barrel prior to deburring and finishing operations as it came off the milling machine. I think I like the way the 10 flute barrel looks better then this one.