(I'm sure this topic has come up before, but I couldn't find it with a search.)

I want to buy a lightweight 16" upper.  The new BM superlight 16" upper looks nice.  My question is what's the pro's and con's between a superlight barrel and a fluted barrel (each 16").

Specifically:

1.  What's the weight difference between the two?

2.  I do a lot of rapid fire practice and I get the barrel very hot.  Is one barrel better than the other for this type of shooting?

Thanks for your thoughts.

The bushmaster super light is a super addition to your battery. However, high round count plinking will prove not to be its purpose as it heats quickly.
The hbar carbine plain or with a brake will be a good firebreather.
You may also consider m-4 handguards ot help with that heat.

Fluted barrels usually cost much more than the Lightweights due to extra machining required. I chose the lightweight over the fluted for that reason. HTH, That's my take on it.

MM419

From Bushmaster:

Barrel (Wt. Lbs.)
--------------------------
16" HBAR (2.7)
16" HBAR fluted (2.3)
16" Dissipator (3.0)
16" Dissipator fluted (2.6)
16" M4 Dissipator (2.3)
16" Superlight (1.9)
16" M4 (2.2)

Thanks for the replies . . .

Would a fluted barrel cool down faster than my 16" Hbar?

What about a superlight barrel?

BTW - I use a vertical forearm grip and that seems to keep my left hand away from the heat nicely.

This is a really tough call because I have both a fluted and a superlight barrel and love them both.


The fluted handles heat really well and would probably suit your rapid fire needs very well.

The light weight is.. well.. light and very handy. It heats up quickly and cools quickly. Shooting rapid fire would probably be okay, accuracy will suffer as things heat up (I've never noticed, but mine is build for CQB).

If you really do A LOT of quick shooting I would suggest the fluted barrel. It's light enough and handles heat the best.

But it's a real tough call. I'm sure you'd be quite happy with either (maybe get the cheaper one [:)]).

You'll probably end up with both anyway!
Lightwieght
[img]http://www.hunt101.com/img/040108.jpg[/img]
Fluted
[img]http://www.hunt101.com/img/047931.jpg[/img]

Thanks Ridge.

Can you expand on your statement that the "fluted handles heat really well."

Does it get hot very quickly?  

My experience has been that it heats up very slowly. Slower than an HBAR, MUCH slower than the Lightweight.

It cools down quicker than an HBAR, but not as quick as the Lightwieght.

The wieght of the Fluted is noticably heavier than the Lightwieght but It is still very managable.

The lightwieght as you see it is 5.6 lbs
The fluted is about a pound heavier.

The fluted HBAR is only about 6 1/2 onces heavier than their superlight according to Bushmaster.  I had a Colt 16" lightweight but traded off for a Bushy  16" fluted for two reasons.  First, in a long shooting session the superlight gets very hot and some barrels bent in combat use.  That's one reason the military went to the HBAR to start with.  Second, I just like a heavier barrel and thought the fluted 16" would save some weight and still be more stiff and give better accuracy than the lightweight.

Oh, and I almost forgot the LCE (Looks Cool Effect)!  See above.

Can someone provide a link to the Bushy 16" fluted barrel, I can't seem to find it on their site.

Thanks...

MM419

The more mass, the more metal, the more metal the more heat it will be able to handle.

Ignore the flutes, they will offer very little thermal advantage. The fluting is not significant enough to noticeably increase any of the three modes of heat transfer. They are flutes and not fins, the surface area is not significantly increased, the exterior ridge is exponentially larger than the interior flute. All that stuff you may hear about bbl fluting increasing strength and improving cooling IS pure BS/hype.


If you want to know which one will cool better to handle more rapid fire, look at the barrel mass table that Hoplophile posted.


No



The Superlight will be worse than the other two.

I own all three, and although I don't have any scientific tempurature measuring devices. I will swear that the fluted barrel heats much slower than my HBAR and cools much faster. It heats very much slower than the lightwieght, and the lightweight also cools down pretty fast, I would say faster than all three.

Less flux in temp is what you want and from my experience the fluted barrel provides this.



This is true you can look at a bushmaster fluted barrel and see that the surface area is greatly increased.

And the truth is is that the fluted barrel is much more rigid than a barrel of the same mass.
Even though I swear it heats slower than the HBAR it will definately heat slower than non-fluted barrel of the same mass.

I think the wieght loss is worth it alone.
and a fluted barrel I think is a better more rigid design than just turning down a barrel to the same wieght.

Plus it looks good. IMO
[img]http://www.hunt101.com/img/040099.jpg[/img]

Goto the barrels section and scroll down. They don't have a specific fluted barrel, but offer it as an option. They have a little blurp about it at the bottom of the barrels page.
[url]http://www.bushmaster.com/shopping/barrel-assemblies/[/url]

Again misleading information.

Only along the long axis of the flutes which is at best maybe 30% of the overall barrell length. So if 100% of the barrel length is fluted, the quoted percentage may be true. (........Depending on the original barrell DIA [%|])

Common sense will tell you that, 180%? Thats almost 2x the surface area.

Realistically, the total barrell surface area has been increased 25%.
Now what does that 25% buy you? Heat transfer has three mechanisms; radiative, conductive and convective. Since the flutes are recessed and a smaller percentage of the circumferance (the opposide of a finned barrell), you wont get much convective heat transfer and THAT is where the money is.
So you get a little better convective and the radiative was already the lowest contributer in the equation.

So lets say for arguments sake that that fluted part of the barrel DOES heat of slower and cool significantly faster.....do you want it to? What part of the barrel has the thermo rate change?? Of course, the part that is fluted!
It's [b]real[/b] advantagious to have a barrel that expands and contracts at different rates along it's long axis.
Ever wonder why match barrels have a uniform profile?

Boomholzer wrote: "It's real advantagious to have a barrel that expands and contracts at different rates along it's long axis.
Ever wonder why match barrels have a uniform profile?"


Boomholzer - two questions:

1.  Wouldn't this situation (unequal heating/cooling/expansion/contraction) also apply to a lightwieght barrel that has different diameters on sections of the barrel?

2.  If the entire or majority of the barrel was fluted, wouldn't that eliminate or materially mitigate the situation?

Thanks.  

chp5,

1) yes it would.

2) yes it would.

It's really a non-issue since the differentials in cooling are not there . I was being facetious. Given the mfg claims, you would think that the fluting added some kind of cryo cooling effect.

In the case of a AR: the added harmonics are no biggie when you have a huge site base and a gas port/tube connected to a non-floated barrel.
The cooling differential is no biggie when you already have a (as you pointed out) a complicated barrel profile.

Base point:
-I would never flute a precision rifle barrel.
-There is no gained avantage except a clever way to remove weight without sacrificing the same rigidity as turning the barrel down.

Don't get a fluted barrel because you want increased cooling capacity, get it when you want a lighter alternative to your heavy barrel.  The effect of fluting for cooling purposes is negligible.  Fluting for a stiffer barrel only occurs when the fluted barrel is of larger diameter than the barrel being compared to.  If you want a heavier barrel, but don't want all the weight, compromise and get the next size up barrel, fluted.  I have a 11.5" fluted HB because I wanted something stiffer than the lightweight, but not the full weight of the HB, and I got a compromise.  The unfluted HB would soak up the heat better, but the fluted barrel would cool faster, not hardly because of the fluting, but because of the decrease in mass.  I have been up, working mostly, for 33 hours now, so maybe I have mistated myself, will edit if someone catches a mistake.

Found a very good barrel article that you might be interested in:

[URL]http://www.varmintal.com/aflut.htm[/URL]

"Only along the long axis of the flutes which is at best maybe 30% of the overall barrell length. So if 100% of the barrel length is fluted, the quoted percentage may be true. (........Depending on the original barrell DIA )"



This is not true the fluting covers the entire length except under the gas block.  so maybe it increases surface area by 160% but still you can see this is a significant inprovement.

It will provide you with a light barrel that handles sustained rapid fire like an HBAR.

Finning does nothing for rigidity but does cool very fast as it increases surface area substantially. Plus it is labor intensive, and not offered.

Fluting increases surface area, lightens weight, aids cooling without sacrificing rigidity.

the best thing to do is add a finned aluminum heat sink like RROC uppers the aluminum transfers heat to the air faster than barrel steel and adds a lot less weight than the additional barrel mass needed to fin steel. This is also sadly not offered.