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

[Maverick223]

I would surmise that the bbl would be stronger in flexure (the primary component of bbl harmonics) when indexed with the "web" (or lack of flute) at 12:00, however I seriously doubt the difference would amount to any perceptible difference at all.

Just to complicate matters I took a look at my DTA-SRS with Krieger bbl and low and behold it has not 6, not 8, but 7 flutes, and is indexed so that there is no flute located at 12:00, but there is one at 6:00. If, and when, I build a new rifle with a fluted bbl, I will probably specify no flute at 12:00, despite the fact that i'll likely not be able to perceive the difference.

 

[Art Eatman]

How much difference in deflection? A millionth of an inch?

 

[Maverick223]

How much difference in deflection? A millionth of an inch?

Probably not far off, Art.

 

[Freedom_fighter_in_IL]

Now I am really glad I have Diamond fluting on my Hart barrels!! This "dilemma" is not a problem with them! Some of you guys need to spend some quality time out of the books. You WAY overthink things. If you were shooting 2500 yards then that 1/1,000,000 inch MAY make a difference of about 1/1000 of an inch in placement. It should be up to the customer and aesthetics.

 

[Sebastian the Ibis]

Having never thought about this before and knowing nothing about metallurgy, I think the only way that the 12:00 flute would matter is if:

1. It was raining
2. The 12:00 flute filled with water
3. You were shooting enough that the barrel heated up significantly
4. The water in the 12:00 flute caused the barrel to heat/cool in a non-uniform manner.

Would this result in a difference large enough to detect? I have no idea, I suppose it depends on how good of a shot you are to begin with.

 

[Dan Carey]

Yes it would. Cool the top of your barrel with a cold water rag and see where the bullet hits.

 

[MCMXI]

How much difference in deflection? A millionth of an inch?

I think the difference would be around three orders of magnitude greater than that! I can run a straight fluted barrel (worse case scenario) in SolidWorks but still haven't figured out how to flute a tapered barrel in that bloody program. I haven't put too much thought into it but did buy a book in the hope that it'll help me figure it out. I won't pretend to know the real-world implications of "indexing" or "timing" a barrel using either of the two approaches, but Varmint Al has some very interesting thoughts/models on this very topic. He has put a lot of work into barrel deflection and harmonics. The difficulty that he and others face is determining what the barrel is doing while the bullet is in the barrel as opposed to once it's left the barrel.

http://varmintal.com/aflut.htm

I thought this was interesting ...

"UPWARD SWING.... The vertical amplitude of vibration is more heavily excited than the horizontal vibration because the center of gravity of the rifle is located below the barrel's centerline and the bullet's travel down the barrel causes a vertical turning moment about the rifles center of gravity. The vertical vibration is most important. Also, the barrel is initially slightly deflected downward due to gravity. When the round is fired, the pressure also tends to straighten the barrel like a bourdon tube in a pressure gage. As the barrel straightens, it over shoots in the upward direction and this adds to the excitation of the Mode 1 vibration. As a side note, the axial extension vibration mode is also probably heavily excited. This is the mode where the barrel extends and shortens axially. But, this axial mode should only have a negligible affect accuracy."

So Mode 1 vibration would have a greater amplitude if the barrel has a greater initial deflection which was my intuition as stated in post #24. I would really like to know WHY gunsmiths and manufacturers do it the way they do. I found some posts yesterday where a few individuals were upset because their gunsmith hadn't "indexed" the barrel at all. In other words, neither the flute nor the "land" were at 12 o'clock. The barrel was threaded on and it stopped where it stopped. Now THAT would really annoy me!!

 

[Maverick223]

You WAY overthink things.

Can we have just one trivial debate over something that only the most devout nerd cares about without naysayers butting in?

BTW, unlike typical straight fluting that diamond pattern fluting is poor engineering design as it is detrimental to strength.

 

[Freedom_fighter_in_IL]

HA!!! But it "shore" is "purdy" and being how it has yet to fail in around 2500 rounds or so I am sort of doubting that "strength" debate as well.

 

[Maverick223]

I didn't say it would fail, or even have a lesser life span, only that it isn't as strong, and there is no doubt about that. Spiral rifling has it's own problems, but it doesn't significantly impact the strength in flexure.

 

[Art Eatman]

"Look! His rifle's got droopy-drawers!"

Sorry. It's just a character defect.

The obvious solution to all this horrendus droop is to use a Mannlicher stock with enough upward pressure at the muzzle to deal with this problem.

But I ain't gonna do the measuring...

 

[Freedom_fighter_in_IL]

Well Mav, My .300 win Mag barrel is Diamond fluted ( I went through a phase for pretty barrels so shoot me) as well. around 3000 rounds through her, still holds less than 1/2moa and I can still, on a good day, cut out the 10 ring at 800 with her. So tell me, where is the "weakness" in the design please? No failure, holds fantastic grouping as long as I do my part, and still is the "purdiest" girl in the locker! And honestly, if they were bad, Hart would not still make them. You wouldn't think one of the top barrel makers would produce bad barrels KNOWINGLY would you?

Like I said to the OP, Seems to me that what should matter in this case is what YOU the customer wants and what is the most aesthetically pleasing.

 

[USSR]

So tell me, where is the "weakness" in the design please?

It's not a "weakness" thing, it simply slightly reduces the stiffness of a barrel, as opposed to slightly increasing the stiffness of a barrel with standard flutes. Hey, if all fluting is to you is a "cosmetic" thing, then it doesn't matter one way or the other. As for myself, I was not enamored with the look of fluting to begin with. I went with fluting strictly for the stiffness and weight reduction it provided me.

Don

 

[Maverick223]

So tell me, where is the "weakness" in the design please?

See the statement above; Don got it right. In more technical terminology the MOI (moment of inertia) is reduced in such a design. If you like it, that is all that matters, but don't confuse aesthetics for a superior design.

 

[Horsemany]

All my fluted factory guns are at 12o'clock flutes. IMO anything else wouldn't look right. It's your gun and your money but I wouldn't want it that way.