View Full Version : Fluted Barrel or Non-Fluted Barrel
ContractSoldier
01-27-16, 09:43
For my lightweight carbine build, I plan on using a Daniel Defense SLIM 15 keymod rail system with a BCM 16 inch enhanced lightweight barrel.
Both the fluted and the non-fluted barrels weigh about the same, with the weight of the fluted barrel being .5 oz less than the 1 pound 6 ounce non-fluted barrel.
My question is, is it worth spending the extra money for the fluted barrel, especially considering the barrels lightweight profile?
HelloLarry
01-27-16, 09:44
All else being equal, a non-fluted barrel will be more accurate.
To me fluting is a negative. If I want a lighter barrel, I'll pick a different contour.
With that shallow of flutes you probably aren't losing much weight.
They will most like shoot the same.
Fluting gives a weight advantage when you have fat barrel, say .90" with little to no loss of stiffness, depending of actual flute design.
From Phreakish:
If we look at the structural equations that relate the stress and strength in a given part we find that the farther material is away from the 'center' of a part the more load it carries. Without getting way technical, this can be related to hollow drive shafts and I-beams and how they're optimized for specific loading. The idea being to put the majority of the material farther from the neutral axis to maximize load carrying.
Using this knowledge, we find that a larger diameter barrel will always be more "Rigid" than a smaller diameter one, all things being equal. Unfortunately, we're limited in how big we can make the ID though. Kind of tough to throw .220 bullets down a .50" ID, right?
What we CAN do though, is flute the barrel. We effectively wind up with multiple 'stringers' that are further from the centerline of the barrel. The result is an increase in rigidity with respect to a barrel of the same weight and profile without flutes. So, we haven't made it more rigid, but it's more rigid than a barrel of a smaller diameter that results in the same weight.
The side benefit is that the surface area is increased. In most conditions, this will result in greater heat dissipation. This typically leads to more heat shed over time, and despite the loss of mass the temperature of the barrel reduces more quickly. Compared to a non fluted barrel, we would expect to see a lower average temperature with the same firing schedule. Since most all materials see an effective reduction in their *modulus as they're heated, we'd expect less POI shift over the course of firing versus a non fluted barrel.
These are generalities though. Too wide a flute, too deep, bad geometry, and a host of other variables can prove these expectations false. Our flutes are designed to take maximum advantage though and are sized to retain stiffness while reducing weight and increasing surface area.
*The modulus of a material is the ratio of stress and strain and will predict the deflection or deformation of a material based on loading. A high modulus means a very stiff material (carbon fiber, for example), a low modulus means not very stiff (aluminum, for example).
https://www.m4carbine.net/showpost.php?p=1946065
HelloLarry
01-27-16, 10:57
Lilja thinks fluting is OK too.
But then you have [URL="http://www.shilen.com/faq.html#question8" and http://www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm who don't think it's such a great idea.
Accuracy Int'l doesn't recommend them either.
Engineers at AI decided to isolate the barrel flutes to see what impact they had on accuracy. The engineers attached a laser to the rifle’s receiver, another to the barrel, and a third to the scope. All three dots were zeroed at the same point, then they started shooting the rifle. They discovered that, no matter which fluted barrel they used, the dots would diverge as the barrel heated. The dots from the devices mounted to the scope and the receiver would stay in place, but the barrel’s device would manifest a point-of-impact (POI) shift. The POI shift from the warming barrel greatly diminished when they used barrels without flutes.
Engineers determined that the flutes never heated evenly, causing the POI shift.
Then consider that when you remove material from the outside of a barrel, button rifled bores get larger and hammer forged bores get smaller where the metal is removed, you can see that it is a crap shoot.
If I was building a rifle to give me the best possible accuracy, I would skip fluting. If I wanted to look cool, I'd get spiral fluting.
ColtSeavers
01-27-16, 11:20
Spiral fluting is the last type of fluting i would ever get, should i be forced to get fluting to begin with as i have no desire or appreciation for fluting to begin with. I always think of an expanding spring when i see a spiral fluted barrel and think about it heating up. When has an uncaptured or guided spring ever expanded straight and evenly in gravity?
Skip the fluting, and have nothing to worry about.
It's really a pretty simple choice. If precision/accuracy is your absolute #1 priority. Buy the fattest, best-profiled, highest quality barrel made.
Everything else will be an extremely small to extremely large compromise from there to get the weight down. You can have certain fluting on certain barrels that still maintains extreme accuracy and you can have the opposite. Your call. Fluting has always been an exercise in dropping weight without going with a thinner profile.
Do the least harm and cause the least change in deflection. Done well, it works. Are you shooting dimes at 100yds with handloads or running around with the rifle, shooting minute-of-man @ 100yds. Or something in between. Buy accordingly.
Ned Christiansen
01-27-16, 11:54
A lot of factory fluting is pretty much ersatz -- decoration only. Like those chromed faux exhaust things you used to see on cars near the top of the front fender, four to a side. Most of it is so shallow, it surely has little effect on stiffness, weight or cooling. Seems like most of the fluted AR barrels I've seen though were a lot "fluteder" than most bolt guns. Can't argue with sources like AI but I've fluted several for a guy who is deep into AR accuracy and I've been a tad on the radical side with them-- got significant weight out with no effect on accuracy according to him. He never commented on cooling. I've weighed before and after but that info is buried who-knows-where..... a quick calculation of the metal removed and steel being at .287 lbs/sq", I'm sure I've taken a pound or so out of some. The Mossberg MVP I saw the other day, I'll bet their fluting took out between 1/8 and 1/4 pound. Which, I'm not saying that's the wrong thing to do from the mfgr point of view.
Long as there's no accuracy penalty, which has been my experience also, I think of it like "it's a smaller, lighter barrel with stiffening ribs added, bringing a slight weight penalty" as opposed to "it's a big heavy barrel that has been somewhat reduced in weight and strength".
ContractSoldier
01-27-16, 11:57
I would like to say thank you to everyone. Lot's of great information.
Both of the barrels have the same profile, but only one is fluted. Sounds like from the posts here, flutted barrels aren't that much of a benefit. Weight saved by going with the fluted barrel isn't a concern as the standard barrel weighs 1 pound 6 ounces which is perfect.
The rail system I'm going with has a lot of open spaces for cooling, naturally I would want to get the most accuracy out of a lightweight barrel for the maximum amount of time. Sounds like I would be perfectly fine saving money and going with the non-fluted barrel.
I haven't seen any thermal imaging proof of heat dissipation.
Simply...
If the barrel cools faster, that is because there's less mass.
More mass means longer to heat up, and longer to cool down.
Less mass means quicker to heat up, and quicker to cool down.
I'm not even sure if the heat-up/cool-down makes a difference, or why it would (metallurgy and ballistics).
Design wise it would makes sense to me to have more metal/strength at the beginning of the barrel, and taper off. In other words, put metal where metal is needed, not where it isn't.
All else being equal, a non-fluted barrel will be more accurate
This is not true, even in a general statement kind of way
If the barrel cools faster, that is because there's less mass
A fluted barrel of the same mass has more surface with which to radiate heat from, increasing the amount of heat the barrel can transfer to the air. It's the same concept as adding cooling fins to the radiator of your automobile
A fluted barrel of the same mass has more surface with which to radiate heat from, increasing the amount of heat the barrel can transfer to the air. It's the same concept as adding cooling fins to the radiator of your automobile
I agree, but car engines have larger fins and air circulation.
And I believe the main marketing feature is fluted barrels are lighter, therefore less mass.
Until I see thermal imaging, I can't believe those little flutes will make a difference. There's just not that much of a surface area increase.
But flutes give the advertisement department something to talk about to differentiate themselves from everyone else.
I haven't seen any thermal imaging proof of heat dissipation.
Simply...
If the barrel cools faster, that is because there's less mass.
More mass means longer to heat up, and longer to cool down.
Less mass means quicker to heat up, and quicker to cool down.
I'm not even sure if the heat-up/cool-down makes a difference, or why it would (metallurgy and ballistics).
Design wise it would makes sense to me to have more metal/strength at the beginning of the barrel, and taper off. In other words, put metal where metal is needed, not where it isn't.
Increasing the surface area will increase the amount of heat lost by a body vs time. However flutes just don't increase the surface area in the hottest part of the barrel that much. If you really need to dump heat, go with a finned barrel.
Keeping a barrel cool is really useful in full automatic fire, it allows a higher rate of fire before cook-offs...
When ever I see a fluted barrel I think custom and extra cash. If that is what you want to exude when showing up to the range by all means go for it. When I settle in on my mat sending 175gr projectiles down range I want my hits to ring clear, don't really care what the guy next to me thinks about how cool my rig looks, more so the occasional "Nice shot" does it for me. I shoot big fat heavy beastly AR barrels with no fluting and spend any extra cash on triggers and other components that actually make a difference in long range accuracy. I respect any builder who wants a nice looking rig, special fluting that no one else has at the range, I think it's like building a show car for some, lot's of chrome and paint. whats the old saying lots of show but no go? As everyone has already said it's all in what your trying to do with the rifle that counts, I got a heavy barrel warm once, it didn't care!
Keeping a barrel cool is really useful in full automatic fire, it allows a higher rate of fire before cook-offs...
Why? What happens?
How hot is too hot?
What are the temp differences between fluted vs non?
How much more helpful is a typical fluted barrel?
I'll throw this in here as well:
https://www.boltcarrier.com/uploaded/thumbnails/db_file_img_363_460x460.jpg
I've had great luck dimpling Noveske barrels with little to no effect on accuracy. While not doing a full-on serious before baseline / after comparison, all the Noveske barrels I've had done are still sub-MOA barrels. That is not my barrel pictured, just something off Google I grabbed. It removed 6oz+ off my 16" 308 barrel and almost 6oz off one of my Afghan barrels. I fully expected accuracy to diminish, but they're still sub-MOA, so I'm fine with it.
Steel warps slightly when over heated, ever over heat your car brakes and feel it in the pedal? Or wonder why your shots walked off paper after stress relief therapy at the range.
I think a well vented fore grip is a wise investment if you have a high rate of fire, its one place to start.
Steel warps slightly when over heated, ever over heat your car brakes and feel it in the pedal? Or wonder why your shots walked off paper after stress relief therapy at the range.
I think a well vented fore grip is a wise investment if you have a high rate of fire, its one place to start.
Will the small extra barrel surface area of flutes/dimples dissipate enough heat to improve accuracy?
And not sure about the vehicle analogy. Today they have cryogenic rotors, which I presume is applied to barrels too.
To me there's a lot of conjecture. It sounds good. There's some amount of truth to the design. But is there enough to make a difference?
Thermal imaging differences between barrels would be the easiest cheapest way to give some proof that there's at least a measurable temperature difference.
I'm entertained by statistically insignificant things, but I also can realize what doesn't make a difference.
Hopefully we'll see a credible review with thermal imaging.
The OP is talking about a fighting barrel not a target barrel. Sheesh! Judging by the OP's choice of rail he isn't trying to squeeze the last 1/2 ounce of weight out of it. I bought the fluted ELW because the 1/2 ounce was worth the bucks to me under the original 8oz 15" KMR. Only he can decide if the weight reduction/cost is of value to him. All of this back and forth over heat/POI shift and accuracy isn't science it's just talk but what do I know?? I only shoot 855s and am perfectly happy if they shoot inside 2MOA.
...the main marketing feature is fluted barrels are lighter, therefore less mass...
The main engineering feature is more surface area for the same mass.
Whether or not the difference is worth it, depends on a variety of factors
ContractSoldier
01-27-16, 16:28
The OP is talking about a fighting barrel not a target barrel. Sheesh! Judging by the OP's choice of rail he isn't trying to squeeze the last 1/2 ounce of weight out of it. I bought the fluted ELW because the 1/2 ounce was worth the bucks to me under the original 8oz 15" KMR. Only he can decide if the weight reduction/cost is of value to him. All of this back and forth over heat/POI shift and accuracy isn't science it's just talk but what do I know?? I only shoot 855s and am perfectly happy if they shoot inside 2MOA.
Correct. My build will be a lightweight carbine.
This barrel.
http://cdn3.volusion.com/j4enh.r2en5/v/vspfiles/photos/BCM-BRL-MID-16-ELW-STD-2.jpg?1447479649
With this rail.
http://cdn3.volusion.com/j4enh.r2en5/v/vspfiles/photos/DD-SLiM-Rail-15-2.jpg?1447479649
Why? What happens?
How hot is too hot?
What are the temp differences between fluted vs non?
How much more helpful is a typical fluted barrel?
What happens?
-The propellant starts to burn before the primer is ignited. The rifle starts to shoot as long as there are bullets in the magazine, without the need to pull the trigger.
How hot is too hot?
- Smokeless propellant has a flash point of around 450° F. That means if the propellant in the cartridge is allowed to reach this temperature, the round will go off. If it is in a locked chamber, it will behave just as if you pulled the trigger.
It won't go off immediately, as the heat has to soak into the brass and then to the propellant, but if it sits long enough it will start to burn.
M16 cooking off video (https://www.youtube.com/watch?v=fO18uWPcnko)
After 300 rounds shot at 1 round per second the surface temperature at the chamber area of a M16 profile barrel will be around 300° F one inch from the bolt face and at 2" from the bolt face, around 500° F. If you shoot 10 magazines in 1 minute 15 seconds (4 rounds per second, you can do that with a semi-auto, if you try), the temperatures are 400° F and 850° F respectively. Those are the surface temperatures, the bore will be considerably hotter.
Cook-offs from that temperature barrel take anywhere from 10 to 25 seconds depending on a few things. (Steel cases take longer to cook-off, another advantage to steel cases.)
What are the temp differences between fluted vs non?
No idea.
How much more helpful is a typical fluted barrel?
More helpful than what? A standard M16 profile or a similar diameter non-fluted barrel?
If you go back to the temperatures I quoted, and look at the size of barrel at 1 inch from the breech face you will see the barrel is just under 1" in diameter (.98" to be exact) and at 2" from the breech face the diameter of the barrel is around .70". That extra thickness accounts for the fact that the surface temperature is almost half. With more material to absorb the heat, the temperature is lower. If the barrel were made .98" all the way tot the gas block, the temperatures would be closer to the lower levels noted.
A fluted barrel, having slight less material to soak up the heat would see slightly higher temperatures, but once you stopped firing, those temperatures would drop slightly faster. By how much? I don't know, but if someone funds me, I'll be happy to try and find out.
The main engineering feature is more surface area for the same mass.
Whether or not the difference is worth it, depends on a variety of factors
I thought it was to have more rigidity for the weight of the barrel.
For examle, bull barrel with deep flutes would have rigidity somewhere between the original weight and end weight, compared to non-fluted barrels. I understand profile and taper is significant as well.
I thought it was to have more rigidity for the weight of the barrel.
For examle, bull barrel with deep flutes would have rigidity somewhere between the original weight and end weight, compared to non-fluted barrels. I understand profile and taper is significant as well.
It does this as well. Search for the Varmint Al links I've put up in a previous thread. They will lead you to an excellent engineering treatise on fluted barrels
Ned Christiansen
01-27-16, 23:36
I did a study on this in about 2000. Not the be-all, end-all mind you. Unfortunately I can't find my notes on it. I ran across them in the last year or so, they'll pop up some day soon and I'll get back to this thread.
I took 3" lengths of 1" diameter cold-rolled steel:
-Solid, sand blasted
-Solid, buffed to a high gloss (I remembered reading in the Machinery's Handbook that polished copper radiates its heat very slowly)
-Solid, painted black
-Fluted, 6 grooves, blasted
I borrowed an IR pyrometer. Don't know if it was a good one or a bad one but it seemed to do what it was supposed to.
I put them evenly spaced between two sheets of 1/2" Transite, an insulating board kind of material. The boards were bolted together, sandwiching the steel pieces, the idea being to not lose heat out the ends.
Heated it all up in the oven-- I think I went 350 and for a couple hours.
I found the top sheet got in the way of taking readings so I took it off and set it all outside for them to cool (summerish, probably 75). I made sure they were lined up so each got the same slight breeze. Took a reading every minute.
And the results.... are yet to be relocated. I do remember a few things: I was sure the black painted barrel would stay hot longer. Even though darker colors radiate heat better, I was sure that the paint would constitute an insulating skin that would outweigh the radiating qualities of black. It did well. I just don't remember exactly how well. Guess Honda had it right when they started painting their race bike engines black.
Between solid blasted and solid polished, no contest, the polished retained its heat longest of all. I know fluted and blasted did better than solid/blasted, it just irritates me I can't remember if it was by a lot or a little. I don't think it was by an amazing amount or I'd remember that.
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