Fluting Barrels

[Bart B.]

Edit: After some more reading I’m going to revise my original answer to your question. In your example the drilled out barrel would be weaker due to losing mass when drilled. I think that in two barrels with the same mass, the one with the larger hole will be stiffer.

Possibly, up to the point where the tube wall is too thin. That's probably past the point of diminishing returns.

 

[3Ackleys]

"I" beams are stronger and stiffer than a piece of solid steel of the same dimensions, same with other types of structural steel. A fluted barrel of the same diameter is stiffer than a solid one of the same diameter.

Take a piece of 1" steel rod, ten feet long, lay it on two horses, one positioned at each end, check the sag. Do the same with a piece of 1" steel rod that is fluted, measure the sag. The solid will sag more. Which one is more stiff?

Still not convinced? How many suspension or other bridges are built with SOLID steel?

There is a section in Brian Litz's new book where they tested a bunch of different barrels. The heavy palma was stiffer than the flutted hvy palma and the non-fluted barrel had less POI movement after the barrels heated up.

 

[Dusty Stevens]

There is absolutely no telling how many shilen barrels ive fluted. Has to be hundreds. But then again ive never needed a barrel warranty either. If i get a bad barrel its just a tomato stake- i never wanted to argue with a barrel maker nor did i want to abuse the policy of them sending me another barrel just cause i didnt think the first one was good

 

[hogpatrol]

There is a section in Brian Litz's new book where they tested a bunch of different barrels. The heavy palma was stiffer than the flutted hvy palma and the non-fluted barrel had less POI movement after the barrels heated up.

I have his older books but would like to see how he arrived at this result. What test methods did he use? Did he shoot the solid barrel then have it fluted to compare or use different barrels of the same contour? Considering every barrel is different, I have to question his methods and conclusions. YMMV.

 

[Dusty Stevens]

A lot has to do with how it was fluted, by whom and how much stress they induced during the process.

 

[Rustytigwire]

Metal is not solid it is flexible.
Its micro structure is as uniform as can be but not perfectly uniform.
Forming raw metal (rolls and whatnot at the mill) makes areas of different density. There are stresses built in. There are varying densities in the same piece. Various heat treatment relieves these conditions to some degree. Not all.
Drill holes in 1/2 or 1 inch mild steel. Hard outsides butter in the middle. Forming rolls refine the outer surfaces more. More density outside.
Barrels are made from good stuff. Not perfect but good as can be made.
If you cut some its different now. Cant go back.
Fluting gives more surface to radiate more heat.
Reduced temp stability exchange for faster cooling?
I just bought a replacement barrel, cheap, solid was not in stock. I bought fluted.
It will be fine for my purpose.

 

[msinc]

Seems if it adds cooking surface, it also adds heating surface. If it cools faster, it would also heat up faster as well.

This is a good point sir, in general though if a given object, {in this case a barrel} can be made such that it will cool off faster {consider functional flutes, as opposed to cosmetic ones, along the same lines as fins in a radiator} then it will also heat up slower because the heat is "leaving" faster as well. All this is of course relative to how fast the heat is being added among other events.
When discussing heat and cool there is this terrible play on words...just like optics. "There is no such thing as cool, only heat...or the absence of it..." or "a scope doesn't gather light", etc.
Here is the problem with flutes affecting a barrels ability to cool: the heat source, the burning of the powder, is happening on the inside, in the bore. The flutes enhanced ability {if designed properly} to help dissipate heat faster off the barrel is on the outside. Said heat has to travel through the barrel wall or body to get to the flutes so it can leave.
The alloy a given barrel is made out of has a number assigned {I believe they call it the thermal number??} that correlates to the alloys ability to conduct heat. Most metals are not surprising in their thermal number...aluminum and copper are both a good conductor and most aluminum or copper alloys are very close in thermal number. Not true of stainless alloys...many are very good conductors, but some are not. Some stainless alloys are very great insulators and resist heat transfer.
The bottom line is that in terms of barrel heat, we feel the outside with our hand and worry about the throat getting too hot. Due to a barrels conductivity this is probably a poor indicator because we need to measure the surface temperature of the barrel right at the throat.
Back to the original heat question, it makes sense to say that if it cools {looses heat} faster then it will {should} heat up slower too.....but the real question with a barrel is always "what's the temperature difference between the outside surface and the actual surface of the throat??" and how much of this difference is due to the barrels ability to loose heat faster or the lack of conductivity's ability to hide the dissipation???

 

[Gene Beggs]

Some think fluting makes a given barrel stiffer.

Others think it makes them less stiff.

What are the opinions and facts?

Bart B.,
This subject was discussed at length on BR Central years ago as a result of Skip Otto's claim that fluting a benchrest barrel made them 'stiffer.' Jerry Stiller of Stiller Precision Firearms got involved in the discussion and did some very professional engineering calculations and many other experienced shooters got involved. The subject was literally beat to death with strong opinions on both sides of the argument.

First of all, understand that I thought the world of Skip Otto who is now deceased. I met Skip over thirty years ago and he had a big influence on my short-range group shooting career. I also know Jerry Stiller very well and have the utmost respect for him and what he has accomplished in both centerfire and rimfire benchrest. Jerry and his right hand man, Curtis Helton made many trips to Midland, TX, to shoot group matches with our club. They are both terrific shooters, engineers and machinists. I built several rifles on their Drop Port Viper actions.

It has been my experience that when experts disagree strongly about something such as this debate on fluting and barrel stiffness, it is usually because they are talking about two completely different things. Yes, and this was the case with the infamous barrel fluting, stiffness thing.

When Skip Otto stated that his barrel fluting made the barrels 'stiffer' what he should have said was it makes them 'droop' less because it removes several ounces of dead weight which reduces gravity droop at the muzzle.

When the experts heard 'makes them stiffer' they immediately said "No way" and went into all sorts of explanations why this was nonsense. Well, of course, what they were thinking was that Skip was claiming that fluting made the barrels "stronger."
And that's not what he meant at all. He meant that his fluting resulted in less gravity droop at the muzzle.

One of the best shooting barrels I ever had was a 22 inch Hart in 6PPC which was too heavy to make the 10.5 pound weight class. I sent the barrel to Skip and he fluted it with his trademark five-flute, 3/8" wide, .125 deep procedure and that thing shot terrific and made me some money at the Super Shoot that year. The thing I remember the most about the barrel is how it 'felt' when fired. It felt as if it had no whip; like it was light as a feather and had absolutely no 'whip.' At the time, I did not understand barrel vibrations as I do now and the only thing I knew was that fluting removed about seven ounces which was what I was after. The fact that the barrel seemed so "stiff" just like a carbon fiber tube, was not understood at the time but I sure understand it now! I knew I was observing something very significant but I didn't understand what it was.

Well, old Skip Otto was right; fluting does indeed make a barrel stiffer, i.e., stiffer as in less droop, it does not make it stronger.

Later,

Gene Beggs

 

[ED3]

This is a good point sir, in general though if a given object, {in this case a barrel} can be made such that it will cool off faster {consider functional flutes, as opposed to cosmetic ones, along the same lines as fins in a radiator} then it will also heat up slower because the heat is "leaving" faster as well. All this is of course relative to how fast the heat is being added among other events.
When discussing heat and cool there is this terrible play on words...just like optics. "There is no such thing as cool, only heat...or the absence of it..." or "a scope doesn't gather light", etc.
Here is the problem with flutes affecting a barrels ability to cool: the heat source, the burning of the powder, is happening on the inside, in the bore. The flutes enhanced ability {if designed properly} to help dissipate heat faster off the barrel is on the outside. Said heat has to travel through the barrel wall or body to get to the flutes so it can leave.
The metal the barrel is made out of has a number assigned {I believe they call it the thermal number??} that correlates to the alloys ability to conduct heat. Most metals are not surprising in their thermal number...aluminum and copper are both a good conductor and most aluminum or copper alloys are very close in thermal number. Not true of stainless alloys...many are very good conductors, but some are not.
The bottom line is that in terms of barrel heat, we feel the outside with our hand and worry about the throat getting too hot. Due to a barrels conductivity this is probably a poor indicator because we need to measure the surface temperature of the barrel right at the throat.
Back to the original heat question, it makes sense to say that if it cools {looses heat} faster then it will {should} heat up slower too.....but the real question with a barrel is always "what's the temperature difference between the outside surface and the actual surface of the throat??" and how much of this difference is due to the barrels ability to loose heat faster or the lack of conductivity's ability to hide the dissipation???

A barrel heats because hot gasses conduct some of their thermal energy into the barrel through the bore.
Fluting the OD has no effect on the bore dimensions, or this energy transfer.
So it's hard to see how fluting effects the heating properties.

 

[msinc]

A barrel heats because hot gasses conduct some of their thermal energy into the barrel through the bore.
Fluting the OD has no effect on the bore dimensions, or this energy transfer.
So it's hard to see how fluting effects the heating properties.

Here is some of that "play on words" thing I was referring to....you could say that hot gases DO NOT conduct anything, hot gases are present and the surface of the bore tries to reach an equilibrium. I believe there is some scientific law regarding this action. I apologize for my current inability to quote it. Every element has a thermal number, the hot gas being the "source" to heat the barrel steel we are not concerned with it's thermal number...we don't care how long it took the heat to go thru the gas itself. Maybe a better way of saying it is that the temperature of the gas is not the problem, it how hot the steel gets that is.
One would hope fluting the OD has no effect on the bore...if it did then certainly no one in their right mind would pay to have it done!!! You are correct {at least I think so} that fluting has no effect on thermal transfer through the barrel wall itself, but it very definitely affects the outer surfaces ability to dissipate said heat once it gets to the surface....again, think of radiator fins. All this is of course given the fact that we have functional flutes and not just cosmetic ones. Flutes or other heat dissipating enhancements aside, there is also this matter of mass itself...a 6 pound piece of steel, no matter the thermal number, will always take longer to cool than a 3 pound piece.

 

[Gene Beggs]

One thing about barrel fluting that I haven't heard mentioned and that is cost! Cost in both money and time.

If you do your own chambering and other barrel work and have the proper equipment, the time and cost factor isn't so much a consideration but if you have to hire it all done, the cost of fitting up a new barrel really increases when you include fluting.

Most of my barrels are not fluted because it does take time. With the light weight stocks and actions available today, making the 10.5 pound LV/Sporter weight is not usually a problem but when you factor in the heavier scopes in use today and the fact that more and more shooters are discovering tuners, there are times when a seven ounce savings in weight is important.

By the way, Bart B., I can understand why some prefer to remain anonymous by not using their full name but I would appreciate an e-mail telling me a little more about yourself. In reading your threads and posts, it is obvious that you are a real professional. I look forward to your input.

My e-mail is genebeggs@cableone.net

I don't use the private message functions here and on BR Central but I look forward to e-mail.

 

[Bart B.]

Well, old Skip Otto was right; fluting does indeed make a barrel stiffer, i.e., stiffer as in less droop,

By stiffer, that means its resonant frequency is higher and will bend less from external forces.

Of course, a fluted barrel droops less. That's not the point most take on the issue. I'm not surprised at your comment. Barrel maker Boots Obermeyer felt the same way.

Mechanical engineers in vibration analysis disagree with the idea that removing strips of metal from barrels makes them stiffer; there's less metal to resist bending. They agree fluted barrels will droop less because they weigh less.

 

[Macropod]

Wouldn't the removal of barrel mass through fluting cause a faster temperature rise?

I think that "x" amount of thermal energy from the combustion process conducted from the bore surface through the the barrel wall would correlate to the amount of barrel steel mass.

Maybe, just maybe, the heat rise being slower with a heavy barrel offsets the amount of heat actually radiated from a barrel that is fluted of the same profile. Over, say, a 10 shot string there would be no advantage in having a fluted barrel?

I'm not talking about weight saving, sag or such here.

 

[msinc]

Wouldn't the removal of barrel mass through fluting cause a faster temperature rise?

I think that "x" amount of thermal energy from the combustion process conducted from the bore surface through the the barrel wall would correlate to the amount of barrel steel mass.

Maybe, just maybe, the heat rise being slower with a heavy barrel offsets the amount of heat actually radiated from a barrel that is fluted of the same profile. Over, say, a 10 shot string there would be no advantage in having a fluted barrel?

I'm not talking about weight saving, sag or such here.

You are correct sir on all points, or at least in certain circumstances you for sure can be. Removal of mass can cause a faster temp rise...but if the thermal number is such then it may not. If the flutes are very effective at dissipating heat then given the way a gun is shot it may not heat up fast enough to exceed what the flutes are dissipating. This is where dealing with thermal events can be so confusing, and that was the point to my previous posts. Things like ambient temp, speed of shots, wind, shade or direct sunlight...these can and will change the dynamics of a barrels heat dissipation.
There are many instances where a fluted barrel, no matter how well designed or functional the flute may be, heat wise is no advantage at all. Very simply, you cannot flute, for example, an M-60 enough to actually make it worthwhile.
I have one rifle with a heavy barrel that is a certain alloy. It heats up on the outside slowly, but when it gets hot it takes significantly longer time to cool back down when compared to my other barrels. This barrel is a harder alloy and supposed to wear less, withstand more heat and last longer. But, I have to wonder if the throat temp is way higher because the heat is staying there instead of being conducted thru to the surface. If this is the case then having it made of this alloy may be of no advantage {given the way I shoot it} because it is getting hotter longer and staying that way at the throat surface. Everything is relative, it likely will last longer than other alloys if I never allow it to overheat.
Flutes to me are like onions. I don't like them, so I refuse to pay any money for either one. I will eat onions if they are there and flutes look good, so I will own/shoot a fluted barrel as long as the flutes didn't cost me.

 

[Bart B.]

If the strips of metal removed by fluting were bonded back on the barrel between the flutes, what would that do to how stiff the barrel is?

 

[msinc]

Whether or not fluting renders a barrel any "stiffer"....I don't know and I don't care. I think it's really a mute point because with or without flutes the barrel is stiff enough. Or at least I have yet to see one that was not. I have straightened a few barrels on a press wheel and it didn't seem like it took any more pressure to do the fluted ones.
Testing or proving it is not rocket science...order two barrels identical except one fluted. Place both in a lathe between centers and press a measured weight on one side with a dial indicator on the other....bang!! Which one deflected the most????
This all sounds simple enough, but I would be more concerned with, as others have posted, how much stress was imparted in said fluting, and what that stress did to the barrels harmonics. Stress that was linear to the bore might show a stiffer barrel on one side, but rotate it on the lathe setup 180 degrees and it might show more deflection, thus skewing the stiffness test. Check it every 45 degrees or so to see if it tests the same all the way around.
All that said, how it affects accuracy is the real question and from that it seems simple enough to just leave flutes out of the equation...but, admittedly the two most accurate barrels I have ever owned were both fluted. One was purely cosmetic having only 6 flutes probably .020" deep. The other had very deep flutes that were wider than the space between them.

Edit: I would add that the people who design for the military have a long running culture which includes a lack of any serious money constraints, a bunch of overpaid, under worked "project engineers" that sit around and dream up {when they actually show up for work} what the "ultimate" barrel should be for our warfighters and they haven't gotten around to adding flutes to sniper barrels yet. If there was any kind of clear advantage at all, however ridiculously slight, they would have been using flutes in the late 70's when they started to take sniping seriously.
That's the military...from a civilian point of view flutes sell!!!!

If the strips of metal removed by fluting were bonded back on the barrel between the flutes, what would that do to how stiff the barrel is?

Sounds like what you describe would increase the diameter, thus making it stiffer.

 

[savagedasher]

And when it all said and done
The real problem is it all hanging off
a action with a thread 1” long and 1” in diameter and that is wher the scope is mounting is .
Merry Christmas All

 

[savagedasher]

Most bolts on a 1” course thread you would need in excess of 300 ft lb
To be tight

 

[richard]

A fluted bbl has more flex than unfluted. It's easy to prove it with your own test. Put your unfluted bbl in a rock solid fixture that is threaded for your action. Set up a dial indicator on the end of the barrel. Zero the indicator and then add some weight to the end of the bbl. Note the reading on how much it flexes.
Take that same bbl and flute it. Do the same test and see for your self what fluting does.

I love fluted bbl.'s They go hand in hand with a tuner.
A fluted bbl with a tuner is easier to tune than a unfluted one. Maybe I should say easier to keep in tune. A bbl that has some flex is a good thing!!

Richard Brensing

 

[muleman69]

It’s my understanding that fluting needs to happen before final lapping. Tim North of Broughton Barrels requires this along with double heat stress relief. If a barrel is finished and shipped to you, and then you get it fluted I can see where a company wouldn’t want that. Tim contours the barrel then sends it out for fluting. Then he double heat treats for any stress and final laps. I had been very happy with Broughton barrels that are fluted. They are hunting rifles.

This does make a lot of sense