Does Fluting a Barrel Make It Stiffer?

[Jim Watson]

Everybody likes to quote Gale McMillan on barrel "break in" but his opinion of fluting doesn't get around much.

[taylorce1]

Originally Posted by Bart B.

If your sundeck is made with 2 x 6 boards vertical set against each other, will it be stiffer if every other one is replaced with a 2 x 4?  

Doesn't matter to me, I'm too cheap to build a deck that way!

It has been my experience that a fluted barrel is still more accurate than most people pulling the trigger.

[Bart B.]

Originally Posted by taylorce1

It has been my experience that a fluted barrel is still more accurate than most people pulling the trigger.

I agree. So are standard barrels.

[Bart B.]

Originally Posted by Bart B.

The most simple reasoning that fluting a barrel makes it less stiff is material was removed that resisted bending. Surely, this is not too hard to understand.

https://web.archive.org/web/20141024...relFluting.asp

Apparently this fact is too hard to understand. I'll try to explain why some other way.

[Kreyzhorse]

Looks cool--like a narwhale tusk.

Or a unicorn horn! Either way, it looks cool.

[TX Nimrod]

I agree. So are standard barrels.

Bart seems to have a relatively low opinion of the shooting ability of “most shooters”. I don’t blame him - unless they “do their part” of course.




.

[LeverGunFan]

Compare a solid round steel bar to a hollow steel tube that has the same amount of material. The cross sectional areas of the bar and the tube are the same, but the cross sectional area of the tube is distributed at a larger radius from the center line than the cross sectional area of the bar. That makes the tube stiffer than the solid bar. If you remove material from the outside diameter of both the solid bar and the hollow tube by fluting, the cross sectional areas are reduced, and the radii to the centroid of the areas are also reduced. That makes the fliuted bar and cylinder less stiff than the unfluted versions.

[Bart B.]

Originally Posted by TX Nimrod

Bart seems to have a relatively low opinion of the shooting ability of “most shooters”. I don’t blame him - unless they “do their part” of course.
.

What percent of shooters can sight in their very accurate rifle without artificial support? Offhand or standing without a sling and only 3 shots.

"Most people" means any amount over half tested.

[std7mag]

If anyone is really in doubt as to reducing weight NOT being a factor on stiffness, but FORM giving more stiffness, go to your nearest overpass.

I can't remember which edition it was, but a few years ago, Racecar Engineering had an in depth article regarding a wheel hub. They removed 1.5 lbs (no small feat for a racing hub!)
but made it 30% stiffer. Same material used, the holes were radioused differently, and ribs put in by removing material.

I've said it before, i'll keep saying it.
Form is a function when it comes to metal.
It's been proven for hundreds of years now.

[Bart B.]

Originally Posted by std7mag

If anyone is really in doubt as to reducing weight NOT being a factor on stiffness, but FORM giving more stiffness, go to your nearest overpass.

This thread is about rifle barrels that are round tubes and changing their outside shape

[Jim Watson]

I saw a piece about a new Army pattern of helical fluting of M4 barrels for cooling.

[big al hunter]

If your sundeck is made with 2 x 6 boards vertical set against each other, will it be stiffer if every other one is replaced with a 2 x 4?

I like your analogy. It is similar to barrels in a couple of ways.

1. It would be less stiff with 2x4s. But the average person walking on it wouldn't notice.

2. The stiffness is dependent on who does the work. If I assemble the deck with every other board being a 2x4, it will be stiffer than if the average office manager did it. I am a professional carpenter and I understand the principal's of woodworking. Likewise, if a barrel maker has lots of testing and practice fluting barrels, they will make a stiffer barrel than a newb. But neither of them will make it as stiff as a solid barrel. And the average shooter probably won't be able to tell the difference.

[TXAZ]

It’s been a few years but we actually addressed this question in a “Solids and Materials” 300- level Engineering class for bending moments.
The math wasn’t simple but the summary answer was:

For the *same weight* of the same material in a linearly fluted and non fluted barrel, the fluted barrel is stronger. (Implies the OD of the fluted barrel is larger by the amount of fluting removed)

For the same outside diameter of fluted and non fluted barrel, the non fluted barrel is stronger.

Caveats:
There are some corner cases (such as the flutes are as deep as the barrel is thick) with opposite results.

[Drm50]

TXAZ is right on, I was trying to figure out simple way to put it but I guess don’t get planer.
The mind bender for a lot of guys is the barrels in question are not the same diameter when you go by weight. I don’t know why they throw this in. When you are talking different diameters it is apples and oranges.

[taylorce1]

I get what Bart B. is trying to teach us. Think twice before you order that fluted barrel. However, I have three button rifled fluted barrels on factory on a M70 EW, one fluted by Twisted Barrel as an after thought to save some weight, and the one by X-Caliber pictured. The two that I'm shooting right now do extremely well, the third hasn't been properly installed yet.

I also used to have a Lilja that was fluted on a 03A3 in .338-06 and I was able fo find a sub MOA load with every bullet I tried. Some were easier than others, but the results were repeatable over several groups (yes some were only 3 shot groups, but many were 5 or more). I traded it to a buddy who makes custom knives, and he's reporting the same results.

[HiBC]

There ia a balance between theory and experience.
I have worked with top graduate mechanical engineering students who had gunfighter quick draw rigs for their engineerng calculators that needed velcro tennis shoes because they could not tie laces. They lacked common sense.
Yet the theory and science has great value.
For 30 years I worked precision machining. A common practice is to rough machine the mass of material away and leave maybe .030 finishing stock,then the piece gets stress relieved,and its re-machined to final dimensions.

If I take a straight round steel bar,or a barrel,draw a straight line the length of the barrel,then along that line ,every 1/8 in,I whack it with a chisel and hammer, by the time I get to the other end,the bar will not be straight.
Its rather basic blacksmithing. The metal gets displaced. That side of the bar grows longer.
Now I can turn the bar 180 degrees,whack down the other side,and the bar will mostly sraighten. But hidden within the bar,are stretched rubber bands of stress.

While it certainly helps to use a sharp cutter,you can buy a brand new top of the line cutter to cut the flutes,but to some degree,it performs just like the chisel I whacked our initial bar with.
Note that carbide insert cutters are actually finished with an engineered radius on the cutting edge. Its "dull" on purpose,because a perfectly sharp edge is fragile.
And thats why the inexperienced rookie machinist might get poor results with carbide. A .003 cut at a .001 chip feed is not aggressive enough to get the cutting edge under the chip. The cutter just rubs. A .030 cut with a .010 chip feed might work much better. FWIW,if you are getting long,stringy,troublesome chips that are like a slinky around your work,try going to a speed and feed chart. I used to cut a lot of 17-4 PH on the lathe.It was a 15 in Colchester. Once I figured out to run a .012 chip feed cutting .100 to .200 off the diameter,the chips came off as tight,blue curls of broken popcorn. The chipbreaker worked perfectly,and those blue hot chips carried away a lot of heat.

I think a lot of folks believe machining heat is the culrit. It may be,to a degree. But each cutting tooth will displace,forge,a little bit of material. That stresses the workpiece.

If you go to Krieger's website,read about the barrel making process,they go to great lengths with stress relief processes along the way.

Fluting is done early. The only process a Krieger barrel sees after final stress relief is the cut rifling and finish lapping.

They don't even thread muzzles after the final stress relief.

Now,I hear you already!! Yes,there are gunsmiths and barrelmakers who do afterthought fluting. No doubt. And many of these barrels shoot world class.

OK. So,is that testimony that afterthough fluting is just fine?

In fact,I'm not a barrelmaker,and I don't have the experience and resources of folks like Bart and Unclenick.. I'm not the authority.

I suspect what goes on is that the muzzle 4,0r5,or 6 inches does not get fluted. Thats the part of the barrel that sends the bullet on its way.

But I believe afterthought fluting will leave a stressed barrel,and it will slightly dimensionally effect the bore under the flutes.
And,as I understand it,a post processing stress relief will effect the surface finish of the bore.

If my goal is a lighter,good accurate hunting rifle,I believe (So what,huh?) that afterthought fluting would be OK.

But if I was pursuing the ultimate, I'd pay attention to the process that works for Krieger.

I'm not saying Krieger is the only barrelmaker, But I'm humble enough to accept they know far more about making barrels than I ever will.And I appreciate that they share the knowledge on their website.

[Bart B.]

Some years ago, I was shopping for a Win 70 sporter. Their on line specs listed both standard and fluted barrels for the model and cartridge desired. Most interesting was their statement saying the fluted barrels were stiffer than regular ones. Yet the weight for both was the same. Off to the local gun shop to make comparisons.

Both versions in 30-06 had identical barrel outside dimensions and profile. Fluted version weighed less.

Called Winchester, told the rep about this. She said that's bad information but she would go on line, find then print that false information and take a copy to marketing and engineering. Then call me and report their comments.

Her callback revealed engineering agreed with her and me; marketing had mixed opinions. Nothing changed on their website for years. Been several since I last checked.

[HiBC]

Many years ago in John T Amber's "Gun Digest" I saw what was supposed to be an ""OOOOOH,AHHHHH " drool over picture of a presentation grade Win M-70 in IIRC, a cartridge with substantial recoil.
I took one look at it,and shook my head in disbelief. While it was a pretty piece of wood..........
If you worked at creating the worst possible example of how to layout the grain through the wrist,exactly how NOT to do it this rifle was it.

Its a lot easier to split wood than break it cross grain. This wrist was set up so the grain ran across the wrist at a quite acute angle,. The grain flowed from the forward point of the comb out the lower center of the wrist.

Who does that? I can only suppose someone who figured the rifle would never be fired,it was just a wall pretty.

Other than for a "look",I don't get spiral fluting of a barrel. I don't have the engineering skills to calculate it,but it would seem spiral flutes would be less rigid. They cross the spine.

Then there is? was? Remington Marketing's three corner barrel.

[Bart B.]

Yes, spiralled flutes remove more metal so it's less stiff than straight ones.

Regarding corregated sheet metal, look at a barrel as corregated sheet metal compressed as tight as possible so there's no clearance between each fold. Weighs the same as a solid barrel.

A corregated sheet metal barrel the same outside diameter but half as many folds will be much less stiff. What about only one fourth as many folds?

[natman]

Originally Posted by emcon5

So someone did test it.

A fluted barrel is less stiff than an un-fluted barrel of the same profile/diameter.
A fluted barrel will be more stiff than an un-fluted barrel of the same weight.

Bingo. In other words, if you take an existing barrel and flute it, it will be slightly less stiff than it was before. (But lighter).

If you take two barrels of equal weight, the fluted barrel will be of larger diameter, therefore slightly stiffer.

[mehavey]

Fluting does not cause stiffness.
Whatever stiffness there is. . . is already there in the original barrel.

-- However --

Fluting removes a significant percentage of the weight,
while retaining a significant percentage of the stiffness.

Think I-beam

[Double Naught Spy]

This thread is about rifle barrels that are round tubes and changing their outside shape

Weren't you the one talking about wooden sundecks????

[Bart B.]

Originally Posted by Double Naught Spy

Weren't you the one talking about wooden sundecks????

Yes, fluting them to change their shape. Not related to rigidity of corregated sheetmetal. Sheet metal is not fluted. It's bent.

[HiBC]

Lets assume there is a person who actually believes you can take any given barrel,...take that particular barrel,and cut flutes in it, to end up with a stiffer,more rigid barrel.....

It might take some doing to help them understand.

How to paint the word pictures?

Folks try using 2x4's,folded sheet metal. OK.

They try.

Then the critics come to blast ideas from the sky like clay pigeons.

But did they bring anything to the table?

[Bart B.]

If corregated sheetmetal is used to make the barrel, how is the rifling formed to seal the bore around the bullet so there's no gas escaping between the bullet and the rounded sheet metal folds when 83,000 psi proof loads are used testing for safety?