Does Fluting a Barrel Make It Stiffer?

There ia a balance between theory and experience.
I have worked with top graduate mechanical engineering students who had gunfighter quick draw rigs for their engineerng calculators that needed velcro tennis shoes because they could not tie laces. They lacked common sense.
Yet the theory and science has great value.
For 30 years I worked precision machining. A common practice is to rough machine the mass of material away and leave maybe .030 finishing stock,then the piece gets stress relieved,and its re-machined to final dimensions.

If I take a straight round steel bar,or a barrel,draw a straight line the length of the barrel,then along that line ,every 1/8 in,I whack it with a chisel and hammer, by the time I get to the other end,the bar will not be straight.
Its rather basic blacksmithing. The metal gets displaced. That side of the bar grows longer.
Now I can turn the bar 180 degrees,whack down the other side,and the bar will mostly sraighten. But hidden within the bar,are stretched rubber bands of stress.

While it certainly helps to use a sharp cutter,you can buy a brand new top of the line cutter to cut the flutes,but to some degree,it performs just like the chisel I whacked our initial bar with.
Note that carbide insert cutters are actually finished with an engineered radius on the cutting edge. Its "dull" on purpose,because a perfectly sharp edge is fragile.
And thats why the inexperienced rookie machinist might get poor results with carbide. A .003 cut at a .001 chip feed is not aggressive enough to get the cutting edge under the chip. The cutter just rubs. A .030 cut with a .010 chip feed might work much better. FWIW,if you are getting long,stringy,troublesome chips that are like a slinky around your work,try going to a speed and feed chart. I used to cut a lot of 17-4 PH on the lathe.It was a 15 in Colchester. Once I figured out to run a .012 chip feed cutting .100 to .200 off the diameter,the chips came off as tight,blue curls of broken popcorn. The chipbreaker worked perfectly,and those blue hot chips carried away a lot of heat.

I think a lot of folks believe machining heat is the culrit. It may be,to a degree. But each cutting tooth will displace,forge,a little bit of material. That stresses the workpiece.

If you go to Krieger's website,read about the barrel making process,they go to great lengths with stress relief processes along the way.

Fluting is done early. The only process a Krieger barrel sees after final stress relief is the cut rifling and finish lapping.

They don't even thread muzzles after the final stress relief.

Now,I hear you already!! Yes,there are gunsmiths and barrelmakers who do afterthought fluting. No doubt. And many of these barrels shoot world class.

OK. So,is that testimony that afterthough fluting is just fine?

In fact,I'm not a barrelmaker,and I don't have the experience and resources of folks like Bart and Unclenick.. I'm not the authority.

I suspect what goes on is that the muzzle 4,0r5,or 6 inches does not get fluted. Thats the part of the barrel that sends the bullet on its way.

But I believe afterthought fluting will leave a stressed barrel,and it will slightly dimensionally effect the bore under the flutes.
And,as I understand it,a post processing stress relief will effect the surface finish of the bore.

If my goal is a lighter,good accurate hunting rifle,I believe (So what,huh?) that afterthought fluting would be OK.

But if I was pursuing the ultimate, I'd pay attention to the process that works for Krieger.

I'm not saying Krieger is the only barrelmaker, But I'm humble enough to accept they know far more about making barrels than I ever will.And I appreciate that they share the knowledge on their website.
 
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Some years ago, I was shopping for a Win 70 sporter. Their on line specs listed both standard and fluted barrels for the model and cartridge desired. Most interesting was their statement saying the fluted barrels were stiffer than regular ones. Yet the weight for both was the same. Off to the local gun shop to make comparisons.

Both versions in 30-06 had identical barrel outside dimensions and profile. Fluted version weighed less.

Called Winchester, told the rep about this. She said that's bad information but she would go on line, find then print that false information and take a copy to marketing and engineering. Then call me and report their comments.

Her callback revealed engineering agreed with her and me; marketing had mixed opinions. Nothing changed on their website for years. Been several since I last checked.
 
Many years ago in John T Amber's "Gun Digest" I saw what was supposed to be an ""OOOOOH,AHHHHH " drool over picture of a presentation grade Win M-70 in IIRC, a cartridge with substantial recoil.
I took one look at it,and shook my head in disbelief. While it was a pretty piece of wood..........
If you worked at creating the worst possible example of how to layout the grain through the wrist,exactly how NOT to do it this rifle was it.

Its a lot easier to split wood than break it cross grain. This wrist was set up so the grain ran across the wrist at a quite acute angle,. The grain flowed from the forward point of the comb out the lower center of the wrist.

Who does that? I can only suppose someone who figured the rifle would never be fired,it was just a wall pretty.

Other than for a "look",I don't get spiral fluting of a barrel. I don't have the engineering skills to calculate it,but it would seem spiral flutes would be less rigid. They cross the spine.

Then there is? was? Remington Marketing's three corner barrel.
 
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Yes, spiralled flutes remove more metal so it's less stiff than straight ones.

Regarding corregated sheet metal, look at a barrel as corregated sheet metal compressed as tight as possible so there's no clearance between each fold. Weighs the same as a solid barrel.

A corregated sheet metal barrel the same outside diameter but half as many folds will be much less stiff. What about only one fourth as many folds?
 
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emcon5 said:
So someone did test it.

A fluted barrel is less stiff than an un-fluted barrel of the same profile/diameter.
A fluted barrel will be more stiff than an un-fluted barrel of the same weight.
Click to expand...

Bingo. In other words, if you take an existing barrel and flute it, it will be slightly less stiff than it was before. (But lighter).

If you take two barrels of equal weight, the fluted barrel will be of larger diameter, therefore slightly stiffer.
 
Fluting does not cause stiffness.
Whatever stiffness there is. . . is already there in the original barrel.

-- However --

Fluting removes a significant percentage of the weight,
while retaining a significant percentage of the stiffness.

Think I-beam
 
Lets assume there is a person who actually believes you can take any given barrel,...take that particular barrel,and cut flutes in it, to end up with a stiffer,more rigid barrel.....

It might take some doing to help them understand.

How to paint the word pictures?

Folks try using 2x4's,folded sheet metal. OK.

They try.

Then the critics come to blast ideas from the sky like clay pigeons.

But did they bring anything to the table?
 
If corregated sheetmetal is used to make the barrel, how is the rifling formed to seal the bore around the bullet so there's no gas escaping between the bullet and the rounded sheet metal folds when 83,000 psi proof loads are used testing for safety?
 
HiBC said:
You lost me there
Click to expand...
Sorry 'bout that.

Trying to learn how a barrel made of corregated sheetmetal would be put together and be both accurate and safe. I don't think it's possible. Way too labor intensive to be competitively priced.
 
Mehavey has it correct. Two barrels of the same size one fluted and one not. The not fluted will be stiffer. So, shooters put on even fatter barrels then flute so they are more manageable. Your store bought fluting is mostly cosmetic. High power shooters for years have fluted their barrels, these flutes are quite deep and by count quite a few of them as compared to the cosmetic commercial made flutes which are few and shallow. Real fluting costs about as much as the barrel. Btw you don’t see benchresters nuch using flutes, they don’t need less weight.
 
Now to add some charcoal to the grill....

Does fluting ( done right as to not stress the steel) add enough surface area to allow for more HEAT dissipation, and thus reduce weight and keep accuracy for a shot or two more by allowing the barrel to cool better?

( assuming good barrel harmonics, and bedding...that is all things being equal which they often are not).

Personally I would not pay more for fluting, but I would not refuse a properly flutted barrel either.
 
I suppose it depends on what you are doing.

You ,might be slow firing a target string,and so surface area and a dissipation rate might matter.

Or you might be a part of a small military team who is breaking contact with a "rolling disengage"

Which involves consecutive full auto mag dumps.

Assuming the fleeing team makes it to an extraction aircraft, cookoff hot barrels are undesirable. Fluting won't keep up, and as far as I know,the best solution is trading the pencil barrel for the additional mass of an H-bar. More heat sink.
 
Good Gravy, this isn’t that hard.

1. Fluting reduces the weight of a bull barrel which if you have ever owned one- is considerable!
2. Fluting increases the surface area so increases heat dissipation
3. Stiffness of a pipe is primarily (on the order of distance cubed) determined by the height top-to-bottom of the force in that direction and much less by the width.

As was pointed out, a 2x8 is bendy in the flat way and very stiff in the tall way and I beams are very stiff in the I way although they have not much in the middle.

Spiral fluting looks cool but isn’t any good theoretically for smooth stress under bends but practically it seems good enough and the looks sell barrels. Theoretically, straight flutes will be stiffer and the stresses distributed smoothly along the whole length but it seems to not matter much.

Having owned some loooong .223 full bull barrels, I would get the next one fluted straight just to taKe some weight off that pipe. Cooling is a bonus. Spiral fluting is pretty but mechanical inferior. A full bull 24” AR barrel is a heavy pipe.
 
I only have a few fluted barrels and that is only because the rifle or barrel was not offered without them. IMO they serve only one practical purpose and that's reduction of weight, but usually that comes with a penalty of reduction of accuracy over the course of repeated shots. Otherwise I avoid them if at all possible--I treat them as "one shot, one kill" from cold bore guns.
 
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