Gunsmithing Barrel Fluting vs Barrel Stiffness

[Bart B.]

Anyone still think fluting barrels makes them stiffer in spite of metal being removed that used to resist bending?

Metal on the top half resisted stretching, that on the bottom half resisted compressing.

 

[seansmd]

Frank had a great podcast recently covering this with bartlein I believe. Ep245.

 

[Ledzep]

Until someone does a proper study that shows that a difference that can be seen through barrel-to-barrel manufacturing noise, it's all theory based and there is math you can do to compare various shapes but IME it doesn't really matter. I've run MTU contours, fluted heavy varmint, fluted rem varm, unfluted #4, Palmas, etc.. etc.. never had a problem with any of them, much less one that I could say "ahh this must not be rigid enough".

 

[Deleted member 113831]

I was touring a barrel manufacturers facility one day. I asked the owner what he thought of fluting.

He told me that all his barrels are hand lapped, and that while hand lapping, you can feel where the fluting begins and ends.

So, he wasn't a fan. He only flutes barrels when specifically requested...and the client can't be talked out if it.

 

[Bart B.]

He told me that all his barrels are hand lapped, and that while hand lapping, you can feel where the fluting begins and ends.

3 barrel makers told me hammer forged barrel's inner diameter shrink a few ten thousandths under the flutes and button rifled barrels expand the same. Cut rifled barrels change half that much either way.

 

[DAVETOOLEY]

Lighter can't be stiffer.
Now barrels the same weight/length- the fluted barrel will be stiffer.
The difference between the two in accuracy will get lost in the noise.
I've fluted #2's just for a what if experiment. They shot just fine.
Fluting adds sex appeal and not much else. It can have an affect on the balance in a good way, particularly in a hunting rifle.

 

[brianf]

Only real piece of info that I believe was AI tested their fluted vs non fluted 5-10 years ago

When the barrels got hot the fluted Groups opened up more.

anything other than that ...dave tooley gave us the answer.

 

[TACC]

Interesting, never knew about accuracy changes when fluting barrels

 

[1moaoff]

A good way to show this would be take a m24 uncut installed in a fixture with high speed film. Film the flex.
Remove barrel
Flute barrel.
Reinstall
Rerun test.

 

[Bart B.]

Mechanical engineers working with vibration issues can calculate how fluted barrels will vibrate at different fundamental and resonant frequencies. 4th order equations used are the same ones used to calculate how much buildings vibrate in earthquakes.

Here's some good stuff.....

Varmint Al's Fluted Barrel Stiffness Analysis

The Real Benefits of Barrel Fluting

 

[BenW]

Fluting a barrel reduces its stiffness, because you’re removing material that resists bending. An I-beam has excellent stiffness (moment of inertia) because the flats are spaced apart, with the majority of the material at the two extremes. A fluted barrel is more like a U channel.
A fluted barrel will be stiffer than an unfluted barrel of the same weight. Adding flutes to an existing barrel reduces both weight and stiffness.
More info here: https://www.engineeringtoolbox.com/area-moment-inertia-d_1328.html

 

[1moaoff]

Mechanical engineers working with vibration issues can calculate how fluted barrels will vibrate at different fundamental and resonant frequencies. 4th order equations used are the same ones used to calculate how much buildings vibrate in earthquakes.

Here's some good stuff.....

Varmint Al's Fluted Barrel Stiffness Analysis

The Real Benefits of Barrel Fluting

My reference was for people that dont believe in math. It seems more people wont believe it without pictures.

 

[krw]

U don’t see BenchRest shooters use Fluted bbls

 

[DAVETOOLEY]

U don’t see BenchRest shooters use Fluted bbls

We/they don't have to anymore. 20" barrels are the accepted norm now on 10 1/2 lb guns. 21-22" is what we wanted back when I was active. Even then fluted barrels were not the norm. Also most barrels were button rifled then. Now we know we can get the same accuracy out of a smaller contour. And target shooters are cheap bastards.

 

[LRI]

Having fluted literally thousands of barrels and also fitting/test firing/delivering the finished product to folks I will say this:

It is extremely, extremely rare (like dying from Covid rare) that barrel accuracy just "tanks" as a result of fluting. If it did, I'd of seen the pattern of behavior and I'd of stopped doing it by now.

As for stiff vs. flaccid discussion:

It is completely dependent upon how you choose to look at it and here is my example. If I have a #3 sporter contour barrel and I waive a magic wand over it and create ribs that are Remington Varmint contour the barrel just got stiffer.

Now, the flip side: If I have a Remington Varmint contour and instead of a wand I grab a tool and machine slots all the way around it and those slots are #3 contour profile guess what? That barrel is no longer stiffer than what it was to start with.

Treat it like this: For those who like fluting, its a means to reduce some weight and make a barrel look cool. Go into it knowing that if this is being done to a rifle that you already have a load developed for, that load is likely to change. You can quote harmonics, whatever. I don't profess to know anything about that. What I do know is that you are changing the mass of the barrel and that alters frequency and amplitude. The load you had working will likely require some revision. What it does not mean is your barrel suddenly went to hell because I (anyone) put all sorts of stress into it.

Unless the nut running the milling machine is using a dull tool and running it backward, there's very little risk of "stressing" a barrel by fluting it. If the steel has been normalized properly it will be fine. ANY premium quality blank offered by any of the vetted/marquee brands will tolerate this procedure all day.

As for benchrest and its self proclaimed "end all" knowledge base: BR guys go through barrels about as quickly as tire changes happen at the F1 race. It can literally be for any reason. Once a "good one" is found, they'll run that thing to the point of failure. Getting that "hummer" though can be expensive. So, it makes zero sense to spend the extra dollars on fluting when there's just as much of a chance of it not making the cut as there is that it will sing an Italian Opera. One has to understand that the BR game is unlike almost anything else done in competitive shooting. It's a very, very controlled, predictable environment that is also very sterile. Using it as the litmus test for other types of shooting is a good way to end up disappointed and with no money in your wallet.

Hope this helps.

C.

 

[jbell]

It is extremely, extremely rare (like dying from Covid rare)
C.

You sir just won the internet today...

 

[eastexsteve]

Only real piece of info that I believe was AI tested their fluted vs non fluted 5-10 years ago
When the barrels got hot the fluted Groups opened up more.

If that's the case, then it must be the removal of material that is having an effect because fluting the barrel causes it to run cooler. I was going to say that's because it exposes more metal to the air, but that's not why. It has something to do with metal density in relation to the bore. But, fluted barrels do run cooler.

 

[DAVETOOLEY]

Minimal difference in cooling. It's not like aluminum finned heads or cylinders on a motor.
Once hot it's going to take awhile to get back to ambient temp.

 

[1moaoff]

If that's the case, then it must be the removal of material that is having an effect because fluting the barrel causes it to run cooler. I was going to say that's because it exposes more metal to the air, but that's not why. It has something to do with metal density in relation to the bore. But, fluted barrels do run cooler.

I think that is over guesstimated.

 

[1moaoff]

guesstimates. After a barrel has been fluted it has less mass so less of a thermal bank. It will heat through faster and cool faster because of mass.

 

[LRI]

If that's the case, then it must be the removal of material that is having an effect because fluting the barrel causes it to run cooler. I was going to say that's because it exposes more metal to the air, but that's not why. It has something to do with metal density in relation to the bore. But, fluted barrels do run cooler.

Not exactly....

If I take a 4x4x4 lump of steel and heat it up to a temperature that is say, 100* above the ambient, it's going to require X amount of time at Y amount of BTU's to do so.

Now you let it sit and return to ambient. Start a watch and data log the time it takes.

Repeat the exact same test on a lump that is 3X, then 2X, and 1X. Guess what? as it gets smaller it takes less time to heat it up and less time for it to cool off. The point here is barrel mass plays into this. So, a fluted barrel will heat up faster because you pulled mass from it. It has to. It will also cool quicker because there's less mass holding onto the heat.

The idea that flutes increase surface area and accelerate the convection is nice to think about, but in practice, it makes almost no difference. If we use any air-cooled engine as the example we see that the cylinders are designed with very thin airfoils that expose a tremendous amount of surface area by comparison. Your fluted barrel is nowhere near that efficient. -Like not even on the same continent of that efficiency.

Now complicate the whole thought process by the fact that roughly 50% of the circumference is shrouded/blanketed by the rifle stock forend precisely where almost all of the heat is generated.

Again, treat it for what it is: Looks cool and reduces some weight.

C.

 

[1moaoff]

Not exactly....

If I take a 4x4x4 lump of steel and heat it up to a temperature that is say, 100* above the ambient, it's going to require X amount of time at Y amount of BTU's to do so.

Now you let it sit and return to ambient. Start a watch and data log the time it takes.

Repeat the exact same test on a lump that is 3X, then 2X, and 1X. Guess what? as it gets smaller it takes less time to heat it up and less time for it to cool off. The point here is barrel mass plays into this. So, a fluted barrel will heat up faster because you pulled mass from it. It has to. It will also cool quicker because there's less mass holding onto the heat.

The idea that flutes increase surface area and accelerate the convection is nice to think about, but in practice, it makes almost no difference. If we use any air-cooled engine as the example we see that the cylinders are designed with very thin airfoils that expose a tremendous amount of surface area by comparison. Your fluted barrel is nowhere near that efficient. -Like not even on the same continent of that efficiency.

Now complicate the whole thought process by the fact that roughly 50% of the circumference is shrouded/blanketed by the rifle stock forend precisely where almost all of the heat is generated.

Again, treat it for what it is: Looks cool and reduces some weight.

C.

You said it so much better.... I only do this from my phone so I wont type long responses....

 

[LRI]

You said it so much better.... I only do this from my phone so I wont type long responses....

The "plus" (I guess) of running long winded toolpath sims is that it can take a few minutes to generate code when I post. That's typically when I troll around on here and stick my nose in people's business.

 

[1moaoff]

The "plus" (I guess) of running long winded toolpath sims is that it can take a few minutes to generate code when I post. That's typically when I troll around on here and stick my nose in people's business.

You need to go over to stupid marksmanship I think it was... guy there saying his 30/06 browning BLR. Yes lever action, shoots sub 1 MOA at 1k...
And check Maggie's for cars you would enjoy and boobies!

 

[Rubicon Precision]

If that's the case, then it must be the removal of material that is having an effect because fluting the barrel causes it to run cooler. I was going to say that's because it exposes more metal to the air, but that's not why. It has something to do with metal density in relation to the bore. But, fluted barrels do run cooler.

Fluting removes mass. A fluted barrel will heat up faster than a non-fluted barrel of equal profile. Using heat dissipation as a selling point for fluting a bolt action rifle barrel is a falsehood.
So no, fluted barrels do not “run cooler”.

 

[Seymour Fish]

Anyone still think fluting barrels makes them stiffer in spite of metal being removed that used to resist bending?

Metal on the top half resisted stretching, that on the bottom half resisted compressing.

No