Fluted barrel orientation on a receiver - flute at 12 o'clock or not?

[MCMXI]

I dropped a new Krieger barrel off to my gunsmith over the weekend for a new build and during the discussion of what was to be done, I mentioned that I wanted the barrel installed on the action such that a flute ISN'T at the 12 o'clock position. This particular barrel has six fairly deep flutes so I want to minimize barrel deflection. My gunsmith told me that he was taught to install a fluted barrel with a flute at the 12 o'clock position since it supposedly improves the harmonics and reduces deflection ... huh!?

So what's your take on this? From a purely engineering standpoint, putting a flute at 12 o'clock would increase the stress in the barrel since stress in a cantilevered beam (barrel) is a function of the length and weight of the beam, the distance from the centroid of the beam to the uppermost surface, and the second moment of inertia (function of the cross section). Deflection is a function of stress. So who's right or is the difference so minimal as to make it a purely aesthetic decision? Is there another reason to put a flute at 12 o'clock.

I have six rifles with fluted barrels. Four have a flute at the 12 o'clock position and two don't. Here's a visual aid.

 

[Boomie]

I think your gunsmith is right. If you are concerned about stiffness in the vertical direction you have to take into account the vertical distance of all the flutes and their cross sectional area (so more area further from the bore in the vertical direction = good). If I did my quick back-of-the-envelope calculation right the flute at 12:00 has a small advantage.

 

[JDGray]

Is the headspacing an issue?

 

[MCMXI]

I think your gunsmith is right.

My gunsmith is in favor of B ... I'm in favor of A. The flute is in relief.

 

[MCMXI]

Is the headspacing an issue?

In what way?

 

[taliv]

i think this discussion is all based on an assumption that is most likely not correct. that is, that the barrel mostly whips in a vertical plane. I think it's possible that it moves in 2 or 3 dimensions, and likely that it moves in a sort of oval motion.

 

[MCMXI]

I think it's possible that it moves in 2 or 3 dimensions, and likely that it moves in a sort of oval motion.

I agree with that statement 100%. I'm convinced (from load development) that a high speed camera would show that the muzzle follows a circular/oval path (due to the the rifling) as the barrel resonates. However, what advantage is there to placing a flute at the 12 o'clock position?

 

[WardenWolf]

Well, it does make initial sighting in a little bit easier, as you can center the sights with the barrel's very visible line prior to shooting.

 

[taliv]

When Knight Armament made the SR-25s, some of them (including mine) were hand-picked barrels that got a little extra attention, as I understand it. They could identify them by a groove at 12 oclock on the muzzle. The significance of that was that also put the gas port in a groove, with the theory being that drilling the hole with a sharp edge that landed into or partially into a land would disrupt the bullet more.

Of course, that has nothing to do with bolt guns, and even less to do with external flutes. I just mentioned it to illustrate how sometimes things get done for pretty obscure reasons that are difficult to guess, so your machinist may be thinking that because the guy who taught him told him to do it that way. And the guy who taught him may have done it that way because he thought it was easy to line up for setting headspace or something

 

[Uncle Mike]

My gunsmith told me that he was taught to install a fluted barrel with a flute at the 12 o'clock position since it supposedly improves the harmonics and reduces deflection ... huh!?

I have 'heard' that also.... do I believe it, I don't!

I don't think there is a creature stirring that could reap the benefit of it if it were true, as slight as it probably would be! lol hehehe

Whatever 'works' for you, is the way I would orient your barrel.

 

[MCMXI]

I just mentioned it to illustrate how sometimes things get done for pretty obscure reasons that are difficult to guess, so your machinist may be thinking that because the guy who taught him told him to do it that way. And the guy who taught him may have done it that way because he thought it was easy to line up for setting headspace or something

This is my thinking too. I can't see any logic or engineering theory behind my gunsmith's standard approach. Both of my POF Rock Creek barrels are oriented as shown in Figure A above, but they both have five deep flutes. My Krieger barrels (installed by Krieger), Remington and DPMS barrels are all oriented as shown in Figure B above. I'm going to do as Uncle Mike suggests and have the barrel installed the way I like unless some actual theory presents itself to convince me otherwise.

Thanks

 

[NCsmitty]

I really don't know the answer, but in thinking about it, I'm wondering if there would be different effects for heat mirage coming off the flutes? I would think the flutes heat faster being closer to the bore heat.
Would "A" be a better choice for putting a full barrel diameter under the scope?
Just a thought, probably meaningless.



NCsmitty

 

[USSR]

D@mn, George, you always bring up such interesting topics. Well, I just checked my Krieger-built, Kreiger fluted MTU barrel (flute at 12 o'clock), and my Terry Cross built Obermeyer fluted AMU barrel (flute at 12 o'clock). Don't know the significance of this, but somehow I don't feel it is just a coincidence.

Don

 

[Uncle Mike]

Kind of makes you wonder how to orient a spiral fluted barrel......whoops!

 

[Jim Watson]

However, what advantage is there to placing a flute at the 12 o'clock position?

I don't think it makes a difference, but if my gunsmith wanted to do it that way, I would let him.

 

[JDGray]

Quote:
Originally Posted by JDGray
Is the headspacing an issue?

In what way?

Shows ya what I know

Didn't know if it would throw off the headspacing screwing the barrel in or out to align flutes, but maybe the chamber is finished after the barrels installed. I'm thinking drop in Savage barrels

 

[Dr T]

On a rainy day, a flute at 12 o'clock becomes a rain gutter...

 

[Captcurt]

Is the headspacing an issue?

It shouldn't be. The barrel is usually short reamed before installation and then the headspace is set with a finish reamer.

 

[Uncle Mike]

but if my gunsmith wanted to do it that way, I would let him

But, the customer is paying for it, and IF the customer specifies he wants a certain 'index' of the flutes, and it 'can' be done, then....

 

[GunTech]

Mostly, flute orientation is a matter of appearance. The important point is that the flute will be in the same position shot to shot, and it is consistency that's the concern. Who care which way the barrel moves microscopically as long as it does it the same way every time.

I'd bet money that in a blind test of flute alignment, you would see no statistical difference. Keep in mind that most rifles are built asymmetrically anyway. The recoil lug is not symmetrical, nor is the receiver shape. This is one of those 'how many angels can dance on the head of a pin' discussions.

 

[rattletrap1970]

I don't buy it at all. A tuning fork resonates the same regardless of it's orientation. I do not believe for one minute that the location of a flute affects that in any way.

 

[desidog]

There are many good points made above. I'm inclined to think that it is mostly aesthetic; since the exact position of a linear flute has little to nothing to do with the spiraled rifling within. The only way i think this would really matter, is looking at individual barrels, specifically at the crown. Depending on where the lands and grooves terminate: this in contrast to the flutes might make for one being better than the other, but i think the difference would be so small as to be irrelevant with my shooting skill. For me fluting is about barrel rigidity and additional surface area for improving heat-loss.

Were there to be a noticeable difference, 6- vs. 8-flute barrels would really matter, due to the different axes, and in the the case of 6-flutes, no 9:00 axis perpendicular to the 12:00.

IMHO, the only thing that matters, besides looks, is Option A reminds me more of a shotgun rib, if you damage your scope and still have a charging rhino to contend with; and as mentioned by DR. T, won't collect water while sitting in a bipod on a rainy day.

 

[Art Eatman]

See Post #21. The issue for tight groups is uniformity of vibration from shot to shot. Where the flute is located shouldn't have any bearing whatsoever on that.

 

[MCMXI]

Thanks for the interesting and thoughtful comments. I'm going to use the orientation shown in Figure A based on the barrel having less deflection (due to gravity) when at rest. This is the only thing I can be sure of and given that the barrel has deep flutes, the deflection could be quite different depending on the orientation. Intuition and engineering don't usually work well together, but intuitively, if the barrel starts out with a larger deflection, the maximum amplitude as the barrel vibrates could also be larger. If the barrel deflects 0.010" at rest (not unreasonable), as a bullet passes down the bore and leaves the muzzle, does the barrel ever deflect more than 0.010" away from the centerline of the bore? The question is whether gravity affects barrel deflection more than the energy of the primer, powder and bullet. Barrel deflection (under recoil) will be a complicated combination of that energy with the effects of gravity.

This discussion may be redundant for many, but I don't want to do something purely because that's the way it's always been done. If you can't provide an intelligent, rational, well-thought out explanation for why something is the way it is, then admit to that. There's no shame in not knowing, there's only shame in not caring ... or worse yet, pretending to know.

Thanks.

 

[Howard Roark]

Indexing the barrel flutes is easy money and has no bearing on head space. Either way the flutes are oriented, the barrel is fitted to the reciever and bolt face before the chamber is cut. This allows setting the shoulder and tenon back for the flute to index where you want it to. This works the same for a Savage, the barrel nut has to tighten up at the correct point for correct flute orientation and bolt face clearance.

After the barrel is indexed, Then it is chambered.

Porting AR barrels in the grove was mentioned. Krieger does this. Robert Whitley has done a study on barrels that were ported in the grove as opposed to on a land. He found that there was more erosion past the port on grove ported barrels as opposed to ports in a land. His theory is that the support offered by the land deters tear-out. Barrels ported either way shoot equally as well.