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Barrel fluting post build affect accuracy?

 
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  #1  
Old 05-01-2005, 07:48 AM
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Barrel fluting post build affect accuracy?

I have a couple fluted barrels that were done by the barrel maker and they shoot great , the question is have any of you guys had any seen proof of accuracy loss when having a barrel fluted after it has been shot? I've heard that some folks lost alot of accuracy , said to be from the fluting releaving strees inj the barrel and opening the bore to irregular bore size making for thight spots.
I ask because the barrel make I'm looking at doesen't offer the flute size I'd like to have
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Old 05-01-2005, 07:59 AM
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Re: Barrel fluting post build affect accuracy?

JDJones,

From my experience I would say this depends on the diameter of the barrel. If your fluting a smaller contoured barrel then I would say you will have some dimensional change in the bore. Say anything #5 or smaller.

If your fluting a heavy barrel, something with a muzzle diameter of .700 and up I have not witnessed much of a problem.

That said, I do not recommend to my customers to have a barrel fluted after it has been manufacturered. Why take the risk for minimal gains.

If done incorrectly fluting a barrel can induce severe stresses so it must be done correctly and stress relieved afterward.

My opinion is have the barrel blank fluted and if you have a factory barrel, shoot it out and then get a fluted aftermarket barrel later.

Good Shooting!!

Kirby Allen(50)
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Old 05-01-2005, 09:36 AM
ds ds is offline
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Re: Barrel fluting post build affect accuracy?

Fiftydriver,

In your opinion which I value very much, will flutting wether it is done before or after laping change bore dimensions when the barrel gets warm, eg when shot.

Putting it another way flutes create thick and thin sections in the barrel. When you shoot the barrel gets hot/warm so simple physics would suggest the thin sections would expand or try to expand more than the thick sections creating an untrue and stressed bore.

Have you, or anyone noticed changes in bore dimensions on fluted barrels when warm compared to cold.

David.
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Old 05-01-2005, 10:29 AM
LB LB is offline
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Re: Barrel fluting post build affect accuracy?

[ QUOTE ]


Have you, or anyone noticed changes in bore dimensions on fluted barrels when warm compared to cold.

David.

[/ QUOTE ]

If the question suggests that the bore diameter increases when "warm", irrespective of fluting, then the simple physics answer is no, unless cherry red, perhaps?

The flute function is to increase surface area to facilitate cooling, as with the fins on a radiator. It is also said to increase stiffness and reduce barrel whip. Generally speaking, the bore remains as straight as it was drilled; in cross section, although it may warp. However, the temperature at which this occurs is beyond warm. Also, most fluting that I have seen is either an odd number, or positioned so that the thin sections are not directly opposed. But, I have not seen enough examples to say that that is a true statement, anything is possible?

Actually measuring the bore when "hot" would seem to be a difficult assignment, but I could visualize the metal expanding in every dimension, length, outer diameter as well as interiorly, creating a slightly more snug bore. LB
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Old 05-01-2005, 11:19 AM
ds ds is offline
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Re: Barrel fluting post build affect accuracy?

LB

Thanks for your reply,

I am unsure that fluting aids cooling anything much, it was part of the marketing hype (fire 20 shots and see how long it takes to cool back to starting temperature, with or without fluting I think it is a long wait). Also fluting will not increase stiffness but decrease it and increase twisting due to torque (that was one of the reasons interupted fluting was promoted) if a fluted and unfluted barrel are of equal diameter. However if barrels are of the same weight then fluting can increase stiffness because a larger diameter can be used for the same weight, but you still get torque.

The question I asked on heated barrel measurement was far from easy to answer, that is why I thougt Fiftydriver would know if anyone, but all help is appreciated.

Interesting thought about barrels gaining length when heated. It has started me thinking about profiles and barrel tunners again.

David.
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Old 05-01-2005, 12:10 PM
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Re: Barrel fluting post build affect accuracy?

LB,

How do you explain a press fit/interferance fit between two cylindrical parts? The part being inserted into a bore is a couple thou larger in diameter and is stuck in the freezer to cold soak, the part that it will be inserted into is warmed (not red hot or even close, just very warm) the two slip together, but when cooled must be pressed apart.

The main point here is, that the part with the bore in it is heated and its inside diameter gets larger, not smaller as it expands. I would not disagree that the part does expand and will get thicker also, BUT its circumferance expands/increases way "more" which creates the larger ID.

When freezing a shaft/race/bushing etc to be placed into a bore its circumferance "shrinks" a small amount, enough that if the interferance fit between part is small enough it will slip into the bore or be tapped in very easily... if done quickly.

Most fluting I've seen done were with even numbers of flutes so that the raised portion between flutes opposed each other, to retain the original barrel's OD stiffness but reduce weight. Stiffness would "not" be retained if a ridge was opposed by a flute and not another ridge. A barrel's stiffness can't be increased by fluting but it can be reduced in weight and retain original rigidness. Much like a steel "I" beam or "H" beam.

IMO a bore will change dimensionally when fluting because of the heat generated during the milling process. The less heat the less change... use lots of coolant and take light cuts. Now, if the barrel will warp when heating up depends on alot of things. Who knows how much stress is already in the barrel when you get it, or if it is symmetrical or not, then how much more you add to it or releive from it isn't likely to be tested by anyone to conclusion. So, cryo treat it? Probably wouldn't hurt.

We do quite a bit of fluting, 12 and 8 sided barrels but never have tested the "before and after" accuracy. I do have my concerns about it though.
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Old 05-01-2005, 12:21 PM
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Re: Barrel fluting post build affect accuracy?

I don't recommend fluting factory barrels, if you have ever wondered why many factory barrels shoot poorly one of the many reasons is because the bore is not in the center of the barrel ,cut off an old barrel (Remington 721 barrel was the worst I have seen) about 6-8 inches from the muzzle you will find the bore is not in the center of the barrel like you would expect. This causes uneven heating of the barrel and all its corresponding problems. Barrels are also affected by the way the barrel is fluted, Horizontal milling machines do put tons of pressure pushing down on the barrel and could cause deformities, could being the important word. vertical mills put very little pressure downward, there pressure is in the cutting direction along the barrel, this reduces the luckily hood of deforming the bore.
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