Fluted Barrels: Good or Bad?

From Remington’s web site page on their Model 700 Varmint SF: Its 26" heavy-contour barrel is fluted for weight reduction while maintaining rigidity and rapid cooling.

From Winchester’s web site page on their Model 70 Extreme Weather SS: The fluted barrel allows us to give you a stiffer barrel profile that does not carry excessive weight.

'Tis interesting that Remington seems to claim fluting their barrel "maintians rigidity" which will be construed to mean its stiffness doesn't change.

Both claims are easy to prove wrong. The barrel outside dimensions for each makers’ standard and fluted ones are the same. That alone proves the fluted ones are less stiff.

If one puts an optical collimator in the muzzle of each, zeros a scope on the collimator then compares the amount of muzzle axis displacement between a 1- pound and 10-pound weight hung on the barrels at the muzzle, they’ll quickly note the fluted barrel bends more than the standard one. That’s seen by the collimator reticule being different distances below the scope’s reticule for each weight.

I’ve often wondered what each company would say to my challenging them on their claims. If I could prove by the above test that fluting barrels makes them less rigid, they would give me the rifle free of any costs. But if I failed, I would pay them three times the retail price for the rifle.

A great web page about fluted barrels:

http://www.fulton-armory.com/\faqs\AR-FAQs\fluting.htm

Check out the post "A engineer's perspective on fluting" by Gryffin on engineering facts.....
 
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Reynolds, the only flutes I know of that made anything good were the smallest ones used in John Phillip Sousa's piece "The Stars and Stripes Forever" when the piccolo's used in a band did their thing in the finale strains.
 
Bart, you know the reason flutes sell is because of their cosmetics. I think they look good on some rifles and horrid on others. I saw a custom barrel a while back that had spiral flutes and diamond hashes cut into them. It looked good. it shot good. Quite sure is shot inferior to an identical profile that was not fluted.
 
I was reading my post #29 and I guess I should've of put what barrel maker post about fluted this is from Krieger

Q: How does fluting a barrel help?

A: Fluting reduces weight while increasing rigidity over an unfluted barrel of the same weight, ie: smaller contour. By exposing more exterior surface area, it also aids in cooling your barrel. On the barrel contours that we will flute, we expect the same practical accuracy out of a fluted barrel vs. an un-fluted barrel as long as it is fluted by us. A note on fluting done by others: We have researched and performed fluting using many different methods over the years and have really perfected the system we use. Like any other outside operations performed on our barrels, we will not be responsible for the results of other methods of fluting performed by gunsmiths/machinists other than Krieger Barrels, Inc.
 
From Winchester’s web site page on their Model 70 Extreme Weather SS: The fluted barrel allows us to give you a stiffer barrel profile that does not carry excessive weight.
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Actually, it all depends on if your starting point is weight or diameter.

If the gun is going to have a 26" barrel and it's going to weigh X pounds then the fluted barrel does increase rigidity. A gun that weighed the same amount with the same length UNfluted barrel would have a less rigid barrel.

Winchester is not lying or wrong. If the issue is weight, they have a stiffer barrel than it would be if it weighed the same amount and was unfluted.

That's how I read their claim. It's a stiffer barrel that is not heavier.
 
Very good information!







Back when I was a drinking man, I got the notion to flute the barrel on one of my AR15s.















Here are the results...














It's not pretty...














4075579170_62d13c8f55_z.jpg
 
Brian, I'll stand my ground on this issue with Winchester. When I talked with them, the rep's said all their 26" sporter barrels for different cartridges that are fluted and non-fluted have the same outside profile dimensions. That was verified by checking them out in a couple of gun stores. Their fluted barrels weigh less than their standard ones with the same outside profiles for the same cartridge and outside profiles.

Both reps agreed with me and said marketing would not change the false statements made in their web sites. They also agreed with me that the fluted ones are less stiff than the regular ones when both have the same outside profile, bore and chamber dimensions. Other folks had contacted them about that fluting issue they put in print as being incorrect.
 
Can't argue with it from that angle but if they were smart they'd come at it the other way... that the gun would either be heavier with the same length barrel unfluted or the barrel would be less stiff with the same weight gun and unfluted barrel.
 
In my opinion, the whole fluting making a barrel stiffer mis-notion came from arrow making. Before carbon fiber took over, the manufacturers began experimenting with fluted shafts. They were not really fluted, but they had inverted ridges rolled into them. They made the arrow much stiffer. They served two functions" 1. they acted like ridges on tin. 2. They actually caused the tube to have a much larger diameter than its finished diameter. Although they look the same as a fluted barrel, the concept is exactly backward. One is adding material, the other taking it away.
 
The key phrase here is "ceteris paribus" (all other things being equal, to-wit: WEIGHT). But all other factors are NOT equal.

No, fluting a given barrel does NOT make it stiffer (it makes it less stiff). But it does make it stiffer than turning down an exact copy of that original barrel to the same weight, but leaving that 2nd barrel with the round profile.

It's all about weight, and tradeoffs.

Yes, fluted IS stiffer *for the WEIGHT*, which is why people do it. It's not stiffer *for the same outside diameter*. Fluting is a proven concept, not a gimmick or "mis-notion", if I understand the meaning you intend to give to that word. If weight were never a concern, no you wouldn't flute anything because the heavier round barrel is stiffer on an absolute scale. But in the real world, weight is an issue - a big issue! Well, it's a *perceived* issue in the minds of the consumer, at least. It's not really a big issue because light weight is for hunters, and hunters only need the one cold-bore shot and etc. - so the logic goes against this trend. But, you've got guys that for whatever reason, want to build a gun which will be both accurate in the field and at the bench - the primary reason being so that you don't have to spend all day at the range waiting for your bbl to cool in order to test the bbl/ammo combination you're trying, sufficiently, without stringing!!

As I said above: Fluting=>Good. CF-wrapped=>Better. But the increased cost goes up exponentially on these two options, for only linear returns (as is always the case - the classic diminishing returns situation).

So, if the reality is that you can't afford either of those, then the choice becomes this: If all you need is first-shot accuracy from a cold barrel (hunting), then thinner is better (#1 contour) - regardless of length. Simple.

But if you want (or "need") to go from 0.75 MOA to 0.4 MOA accuracy with quickly-repeated shots from a hot barrel (note that virtually no one "needs" that), then you need the barrel thickness that gives you the correct stiffness, which in turn depends on length. If it's a 20" bbl, you don't need but maybe 0.7" or .8" or so to give you utmost stiffness which accomplishes your accuracy goal (depending upon bbl quality of course - and chambering and how fast you're shooting). But if it's a 29" bbl, you might need 1.0" or more to achieve the same stiffness as a 0.8 / 20" bbl. That adds a LOT of weight, because it's both longer AND thicker, and those two are multiplied to get total weight.

But then again, the longer the barrel, the more absolute quantity/mass of steel, and therefore the more absolute cubic area of heat sink available, as well as giving you more surface area to dissipate heat. Which means that the curve is *slightly* skewed back toward less-thick the longer you go.... you still have to go thicker to get equal stiffness, but you may not need quite as much stiffness (i.e. may not need *equal* stiffness to accomplish the heat-dissipation rate you need), if the heat dissipation is enough to keep the bbl from tweaking as you go longer (depending on how fast you shoot and how much powder is burned by your chambering choice, and thus how much heat is generated - both per shot and cumulatively). So that's why you don't need a 2" thickness on a 29" or 30" length... but you just *might* need 1.0" or 1.2" diameter to attain the needed stiffness for hot-barrel sub-0.5 MOA accuracy at that extreme length.

This is why 300-yard benchrest comp. participants use 20, 21, or 22" bbls and use a PPC round that doesn't generate too much heat per shot - they have weight classes which rules out ridiculously-ginormous thicknesses, so they go shorter to get the stiffness they need to handle the heat, based on how fast they have to shoot the strings in their comps. The quintessential benchrest rig uses a 20" bbl in 6mm PPC, and could turn in 0.2 or 0.3 MOA groups at 300 yards from a good shooter! (or at least, that used to be the case).

And relatedly, for your viewing pleasure, here are some rail guns with extreme thicknesses for ultimate stiffness & accuracy, getting in the 0.15 MOA range groups at 200 yards (not sure the length on these bbls though):

http://www.youtube.com/watch?v=6qatf5g7lzk

http://www.youtube.com/watch?v=Yv274JUfSOg
 
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The quintessential benchrest rig uses a 20" bbl in 6mm PPC, and could turn in 0.2 or 0.3 MOA groups at 300 yards from a good shooter!
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I agree. Once in a while they'll do that. But what about the groups that are larger?

I've not seen anything that shows any benchrest rifle used at 300 yards shoots better than about .4 MOA at its best. The NBRSA 300 yard, eight 10-shot group agg. is about .27 MOA. As that's the average group size, the biggest group shot is larger; probably up in the .4 MOA range or bigger. Nobody else has shot 80 bullets that well in a benchrest match. So luck played a big part in that record. All the other groups are much, much bigger.

I've seen test targets from Win. 70 based match rifles chambered for .308 Win with 26" heavy barrels shooting at 600 yards with groups under 1 inch; that's in the .16 MOA range. And ten or so 10-shot groups all under 1.5 inches, .25 MOA at the same range from the same rifle. Plus a 40-shot group at 1.92", under .3 MOA that same time. All shots fired about 20 to 25 seconds apart.

Short stiff barrels are no more accurate than long whippy ones. Every barrel whips and wiggles at its same exact resonant frequency (and even harmonic multiples thereof) for every shot fired. There is no difference in the accuracy attainable with a 30 inch, long slender 7/10ths inch thick 5 pound barrel in a .308 Win. Palma rifle and the same length 15 pound 1.3" thick and much stiffer benchrest rifle barrel. The best of both will keep all shots under 5 to 6 inches at 1000 yards and no better with good ammo and shooters in like conditions. (Check out the LR records and see what the biggest groups are for many-group agg's.) Of course, once in a while they'll cluster 5 shots into about an inch, but that happens only a few times in the life of each barrel.
 
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Short stiff barrels are no more accurate than long whippy ones.
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Well, yes, and no...mostly yes that is right. They are no more accurate when the temperature of the barrel at the time of the shot is the same from shot to shot. But as you know, if the temperature is different, that is mostly not true, as a general rule. Barrels can and do bend under heat, which changes barrel harmonics leading to stringing or worse. Which is why thicker/stiffer bbls are used in competition, where multiple shot strings heat the bbl and don't give it time to cool. As well as "tactical" rifles, where one might in theory need to shoot a rapid string or even semi-rapid.

But yes, exactly - from a "cold bore" (which could really mean from a cold bore, or from a warm bore, or from a hot bore - doesn't matter which as long as it's the SAME every time), a pencil bbl is just as accurate as a 2 incher, ceteris paribus (bbl quality, ammo, etc.).

Temperature, both ambient (i.e. case & powder) and barrel, are very important to accuracy, but a stiffer bbl *minimizes* the effect of one of those two (bbl temp), by minimizing the changes in bbl harmonics, by resisting bending, as I'm sure you know. Of course, very high bbl quality resists bending too, by being more uniform, so the general rule has less effect with the highest quality bbls, but the rule still applies. If it didn't, every benchrester and rail-gunner would use a #1 or #2 contour (why waste steel for no reason?).

Thank you for correcting me on benchrester typical accuracy - more like .3 to .4 ish MOA from the best shooters, rather than .2 to .3 ish - yessir, I will buy that. At least at 200 to 300. At 100 yards, .2 to .3 MOA is more like it, with less wind wildcard effects.
 
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Dremel sez:
But as you know, if the temperature is different, that is mostly not true, as a general rule. Barrels can and do bend under heat, which changes barrel harmonics leading to stringing or worse.
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No, I don't know that nor do I believe that. Not if the rifle's built right. Nor does hundreds (thousands?) of other competitive shooters using 30" long, thin whippy barrels starting with a cold barrel shooting one shot every 20 to 30 seconds apart 20 to 30 times and not having any change in point of impact relative to point of aim.

Barrel steel doesn't change its rigidity enough as it heats up firing shots that fast to change point of impact. If it did, then arsenals testing match ammo with 250 to 300 shot test groups would see changes in bullet impact as barrel temperature changed. David Tubb is one who shoots more rounds per minute in long range competition than anyone else I know of; especially in quick changing wind conditions. More than once, I've watched him as I kept his score start out with a cold, long, skinny, very whippy and flexible barrel shooting at 1000 yards. He never touches the elevation knob for a 20-shot string fired in 5 minutes or less. And his windage knob was only turned to correct for wind changes. Same for other top ranked long range competitive shooters firing shots almost as fast as he does.

What about high power match rifle competitors shooting rapid fire matches with 10 shots in 60 or 70 seconds from sitting or prone. Starting with a cold barrel, proper tests have proved the rifle will shoot 1 inch 10-shot groups at 300 yards, but when fired from the shoulder 3 inches at 300 is as good as they get.

But then folks who do this use barrels fit to the receiver such that they don't bend as they expand microscopically from heat. Something that no factory rifle I know of does; so their barrels typically change point of impact as they heat up. Not to mention any dimensional change the receiver has as it heats up from being hard pressed against the barrel.

Best example/test I know of is when 40 shots were fired from a .308 Win barrel at 600 yards about 15 seconds apart; they all went into less than 2 inches; starting with a cold barrel.

Heavy barrels are used in competiton because that extra weight enables the rifle to move less while the bullet goes down the barrel. This helps when the rifle's held by humans; when clamped in a machine rest or fired in some other free-recoil system, barrel weight does nothing for accuracy.
 
tried to stay out of this one, butttt.....

The post comparing the wood deck is kinda way the heck off!! While there is a "grain structure" to metal, how those grains are oriented has a lot to do with stiffness.

Form is function in metal.
Example...
Take a piece of flat metal, steel or aluminum, not the stiffest.
Now take same piece of metal and put it in the break and give a tweak to put a small raised "x" across it. Much stiffer!!

Again piece of flat metal, now drill 3" holes in it. At the edges of these holes, we are going to raise a lip. Much more stiff than either the flat plate, or the plate with the raised "X". Also much lighter.

As was mentioned earlier about bead blasting adding area. This would tend to relieve any stresses that were place in the metal also. AKA Peening..

Then there is the whole heat treating methods..

Lastly, who is saying that the fluting is done AFTER the bore has been done??? And if it was properly stress relieved/ heat treated???


Ok, getting off my soap box and resuming oogling Kate Upton pics....:D

Errrr I mean googling....
 
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Filling in flutes on a barrel makes it less stiff???

Take a piece of flat metal, steel or aluminum, not the stiffest.
Now take same piece of metal and put it in the break and give a tweak to put a small raised "x" across it. Much stiffer!!
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"The Rigid Roof Analogy" in

http://www.snipercountry.com/articles/realbenefitsbarrelfluting.asp

Effectively squelches the above concept. It puts more metal mass at right angles to each ridge for a given measurement across them. The dimensions of the sheet will be smaller if the metal in the X is the same thickness.

Change my example of a deck made with wood board to type 316R stainless steel rectangular bars and the results will be the same.

I know that it's hard for some folks to accept the simple fact that removing metal along the length of a round bar takes away metal that resists bending. With less resistance to a force at right angles to it, that bar will bend more for a given force applied at right angles to its length. You've removed part of the thick ends of 6 pie slices of metal around that barrel with 6 others still the same shape for a barrel with six flutes.

What if a fluted barrel had all that metal replaced back in the flutes making it the same as it was before fluting? Would it now be less stiff????
 
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The post comparing the wood deck is kinda way the heck off!! While there is a "grain structure" to metal, how those grains are oriented has a lot to do with stiffness.

Form is function in metal.
Example...
Take a piece of flat metal, steel or aluminum, not the stiffest.
Now take same piece of metal and put it in the break and give a tweak to put a small raised "x" across it. Much stiffer!!

Again piece of flat metal, now drill 3" holes in it. At the edges of these holes, we are going to raise a lip. Much more stiff than either the flat plate, or the plate with the raised "X". Also much lighter.

As was mentioned earlier about bead blasting adding area. This would tend to relieve any stresses that were place in the metal also. AKA Peening..

Then there is the whole heat treating methods..

Lastly, who is saying that the fluting is done AFTER the bore has been done??? And if it was properly stress relieved/ heat treated???


Ok, getting off my soap box and resuming oogling Kate Upton pics.
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And fluting a barrel does not make it stiffer, whether you do that before the bore has been drilled or not.

Folding or scoring sheet metal increases stiffness because you are redirecting material from the X plane to the Y plane, in essence you could get the same effect by adding material to that plane, which is a poor analogy for fluting which is material removal.

But some myths will never die.

Jimro
 
I can't disagree with that article except that he, once again, approaches the "it makes it stiffer" argument from the radius rather than weight direction. It only makes sense to look at it from that side if you're trying to make argument against fluting.

Most people are concerned about weight. There's threads running on here all the time about light hunting rifles. Looking at it from a weight perspective, which makes the most sense for most situations, a fluted barrel IS stiffer.

I don't care that the barrel could have been heavier and stiffer. I care that it's stiffer than it would be for the same weight, because heavier doesn't help me.
 
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