Effect of Fluting on Barrel Harmonics

[savagedasher]

Take two identical pieces of square steel bar stock Cut large grooves on opposing sides of one. Now you have an I-beam. Did it magically become stiffer than the solid square bar stock? No.

Take two identical pieces of round steel bar stock. Drill a hole lengthwise all the way through one. Now you have a pipe. Did it magically become stiffer than the solid round bar stock? No.

As CatShooter correctly pointed out, the cooling rate of a barrel is proportional to its surface area/mass. Unless the grooves are cut extremely deep (think cooling fins), the amount by which it increases the surface area/mass will be quite small.

My 1.298 barrel putting blue painters tape on the diameter was 3'' .900 When I did it in the flutes it ended up being 1'' 400 longer. That would be all surface for extra cooling. ;D ;D ;D Larry

 

[CharlieNC]

Both the Varmint Al and Chris Long OBT analyses suggest the harmonics associated with stiffnesss (up/down & sideways) are secondary in importance to the pressure wave that goes back and forth from breech to muzzle. On this basis the barrel length would be more important for tuning than diameter. Of course anything can get screwed up, like from a bad fluting job. I'm sticking with my fat barrels.

 

[ericbc7]

I got into a similar discussion on another forum a while back, and realized that my civil engineering background was not applicible to barrel response. Columns can maintain stiffness with flutes, barrels behave differently. Stiffness in terms of barrels means resistance to expansion, not flex like columns. In barrel terms the forces expanding the barrel are resisted by the material as a function of the surface area and distance from the bore centerline I believe. In other words the resistance to "bulge" is greater on a solid 1 inch dia barrel than a fluted 1 inch od barrel. Cooling is complicated and depends on material, surface area and differential temps.

The only thing I'm sure of is that I'm not an expert lol.

 

[LHSmith]

FWIW, a fluted barrel will heat up faster during rapid fire ( as in most matches) than an unfluted barrel of the same contour.

 

[chkunz]

Varmint Al has it covered .Reducing the weight of a barrel by fluting makes a stiffer barrel then reducing the weight by decreasing the diameter. Larry

Also true.

 

[chkunz]

Varmint Al has it covered .Reducing the weight of a barrel by fluting makes a stiffer barrel then reducing the weight by decreasing the diameter. Larry

Larry, that is correct. Fluting makes a stiffer barrel than and un fluted barrel of the same weight.

Also true.

 

[chkunz]

To settle the "Stiffness" debate...

2 barrels of the same outside DIAMETER... one fluted, one not, the UN-FLUTED one will be stiffer.
2 barrels of the same WEIGHT... one fluted, one not, the FLUTED one will be stiffer

https://www.youtube.com/watch?v=cSMwCXO2gbU

Both true.

 

[chkunz]

The mechanics of materials as defined in any mechanical engineering textbook on the subject are well defined and understood by those who study the subject and the engineering principles are applicable to the questions of barrel fluting and stiffness. Within limits, not including fins for example, fluting will provide a stiffer barrel of the same weight by allowing a larger diameter for that weight. The parameter in the equations that deals with this is called moment of inertia. So the question of stiffness is an easy one to answer with the laws of physics, what is not easy is the question of accuracy, specifically can accuracy be improved in some way by fluting? I would like to see some definitive data on this, it may exist but I have not been able to find it. I have found a lot of opinions that seem to be based on erroneous engineering concepts. Heat transfer is another well defined engineering subject and as it applies to rifle barrels the increase in surface area from fluting, although small, is favorable but the removal of mass is unfavorable. Roughing up the surface would probably be more effective at increasing heat transfer or painting the surface black. Unfortunately we are not dealing with a steady state condition for heat transfer as it applies to this problem and the solution is not simple.

 

[FatBoy]

See what you have all done now.... You have brought out T Rex's inner engineer. We have been working 14 years of steady suppression techniques to quell this behavior and you've all ruined it.

Thanks.

 

[chkunz]

See what you have all done now.... You have brought out T Rex's inner engineer. We have been working 14 years of steady suppression techniques to quell this behavior and you've all ruined it.

Thanks.

OK, it is back to rehab for me.

 

[FatBoy]

See what you have all done now.... You have brought out T Rex's inner engineer. We have been working 14 years of steady suppression techniques to quell this behavior and you've all ruined it.

Thanks.

OK, it is back to rehab for me.

Recoil therapy?

 

[FatBoy]

See what you have all done now.... You have brought out T Rex's inner engineer. We have been working 14 years of steady suppression techniques to quell this behavior and you've all ruined it.

Thanks.

OK, it is back to rehab for me.

Recoil therapy?

Just make sure it's a fluted barrel. The lighter weight will slightly increase recoil, thus enhancing the therapeutic effect ;D.

Well played sir.

 

[Minesweeper3433]

I have a single blank that is fluted that I plan on doing a tactical rifle with only to help offset the higher weight of the suppressor I use on the end. Having a HV contour barrel with a big can on the end is almost always muzzle heavy to an extreme that bothers me. So I decided to give the same contour a try with very heavy fluting for most of the barrel.

 

[Rustystud]

After reading this post, I have determined several of the posters got their engineering degrees from different schools.
In my 50+ years experience with barrels I am of the opinion fluting can have little and/or no effect, or completely wreck a barrel.
The steel, and the stress relieving, the straight drilling, reaming, and pre and post lapping have the greatest deal of effect on barrel performance.
Recently I chambered a 30 caliber MullerWorks 26", AMU contour, 1:10, 4 groove "modified lands" barrel. With Lapua .308 Win brass, 50.5 GRS on W-748, Wolf LR primers and Barnes Tipped Triple Shocks I shot three sub .2 moa 5 shot groups at 100 yds. I shot a 5/8" 5 shot group at 500 yds. I fluted the barrel 4" from the tenon end to 3" of the muzzle, .080" deep with 6 .250" wide flutes. I made the flutes in one pass cutting slowly with flood coolant. I have shot this barrel since fluting, it continues to shoot sub .2 moa. I can't see any I'll effect from the fluting. This fluting removed almost a pound of weight from the barrel and it looks very good to the observer. I have seen lighter barrels that were not properly stress relieved look like bananas after fluting.
The important thing is knowing the metal and how it has been treated. It also is important to know the process taken in completing the fluting.
Nat Lambeth

 

[Trevor60]

I have looked into fluting and based on my research found that fluting a barrel will produce less vertical then an un-fluted barrel. I have shot heave palma barrels for F/TR for my last 3 and wanted a stiffer barrel of the same weight so i went to fluting. According to computer modelling and limited anecdotal evidence there is a real benefit to fluting barrels.

you will note these are sine wave images. but they illustrate my point

Here is the heavy palma barrel

here is a fluted heavy palma barrel

You can see the fluted barrel has less swing from top dead centre to bottom dead centre. With a smaller overall swing for the entire cycle you improve your vertical by the simple fact your barrel will swing through its cycle more frequently giving you a higher probability your bullets release near or exactly the same as your previous shot.

Now i know most or all of you strive like me to tune a load so your in the top or bottom 1/10 of the swing cycle giving you an even greater grouping ability

That is how i understand it and is the basis for testing my first fluted barrel

Trevor

As for the AI doing extensive testing and abandoned fluted barrels I heard AI used button rifled barrels and as we know there is a whole host of issues with stressing button barrels as opposed to cut rifle. (IMO)

 

[chkunz]

I have looked into fluting and based on my research found that fluting a barrel will produce less vertical then an un-fluted barrel. I have shot heave palma barrels for F/TR for my last 3 and wanted a stiffer barrel of the same weight so i went to fluting. According to computer modelling and limited anecdotal evidence there is a real benefit to fluting barrels.

you will note these are sine wave images. but they illustrate my point

Here is the heavy palma barrel

here is a fluted heavy palma barrel

You can see the fluted barrel has less swing from top dead centre to bottom dead centre. With a smaller overall swing for the entire cycle you improve your vertical by the simple fact your barrel will swing through its cycle more frequently giving you a higher probability your bullets release near or exactly the same as your previous shot.

Now i know most or all of you strive like me to tune a load so your in the top or bottom 1/10 of the swing cycle giving you an even greater grouping ability

That is how i understand it and is the basis for testing my first fluted barrel

Trevor

As for the AI doing extensive testing and abandoned fluted barrels I heard AI used button rifled barrels and as we know there is a whole host of issues with stressing button barrels as opposed to cut rifle. (IMO)

Would you please add information to the horizontal and vertical scales so that we may compare these two graphs.

 

[dcali]

"Which is stiffer" is the wrong question. Cutting flutes into a barrel will make it less stiff. This is inarguable and settled. But what does it mean? It means if you hang a weight on the end of the barrel, it will deflect more. That's all.

What we care about is the rifle's dynamic response to the bullet firing - how does the barrel "whip" when fired. This response (which is *not* the sine wave "modes" so many refer to, but rather something much more complex) depends on the stiffness of the barrel AND the weight of the barrel. Removing weight makes the barrel whip faster. Removing stiffness makes the barrel whip slower. Fluting, overall, will make it whip slower, because the material removed happens to add more stiffness than weight.

But you won't know if you want more or less stiffness until you try it out. It's not something you can say is always good or always bad. It's just different.

If you want to play with barrel vibrations, carefully selecting length (which has a HUGE impact on barrel stiffness) or adding a well designed tuner makes more sense. There is less to go wrong, you have more control, and you don't waste money on fluting an expendable part.

 

[Trevor60]

the sine waves were illustration only and pulled images from the internet, they are simply my understanding of how a stiffer barrel would vibrate against a whipper barrel.

As for using a tuner, i am in agreement (now) a tuner would seem to be the better option and give you more flexibility to tune or fine tune a load for utmost accuracy.

BUT if you don't try different things the sport doesn't move forward

 

[LHSmith]

And a lighter weight barrel than the fluted barrel will have an even flatter sine wave. FWIW from Ratigans book Extreme Rifle Accuracy: "As rifle weight increases, the amplitude of the vibration increases - but the frequency does not change." He goes on to say that the tune for a heavier rifle has a sharper peak. However, don't neglect the fact that heavier rifles are usually easier to shoot because of the extra weight (more forgiving of errors in the shooters form while executing the shot) combined with the bonus of not heating up so quickly.....+ typically heavier barrels will shoot accurately at a higher node than a lighter bbl. will.

 

[Ggmac]

Removing metal does not make it more rigid , fluting as done now is for looks only , it has no measurable cooling , the flutes are in the wrong direction ( think cooling fins ona motorcycle )
Any cuts on the barrel would have to be exactly the same depth , exactly the same width and cut exactly the same # of degrees around .
A lot of info on it in old Prec Shoot magazines , books , precision shooting at 1000, bench rest primer and another I can't remember . All answers were from top barrel , rifle manuf.