Does fluting on a AR rifle barrel really worth the cost???

[ShootAndHunt]

Visited Bushmaster website recently and notice that they have the barrel fluting (machining lengthwise grooves into the outer surface of the barrel) option for their AR rifles. They listed three advantages of barrel fluting:

1. increased radiational cooling of the barrel

2. adds to the "stiffness" of the barrel which enhances its accuracy

3. the barrel is lighter after machining removes the steel in those lengthwise grooves.

in conclusion, they said: " A fluted barrel will last longer, shoot straighter, and is considerably lighter than a standard heavy barrel. The accuracy gains would be most noticeable at longer distances or to the competition shooter."

Have no any experience with a fluted barrel, I got the following questions after reading this:

1. Point 3 sounds obvious, but how much weight could the fluting reduce on a AR rifle?

2. Point 1 seems reasonable too, but do these grooves introduce the uneven cooling (just like the octangle barrel)??? (which could bend the barrel slightly and lead to inaccurate shooting).

3. Point 2 is the most confusing, could anyone tell me whether the fluted barrel is really "stiffer" than a unfluted one and hence shoot more accurately???

How many grooves does Bushmaster make on a flutted barrel, are they long enough to be visible ahead of the handguard?

 

[Onslaught]

Before I say this, let me mention that I LIKE and OWN a fluted bushy...

But their "opinion" of their fluted barrels is at least "misleading".

1. increased radiational cooling of the barrel

TRUE

2. adds to the "stiffness" of the barrel which enhances its accuracy

FALSE - what it does is, for the same WEIGHT barrel, a fluted barrel would be stiffer than, say, an A2 profile. A non-fluted HBAR would be stiffer and stronger than the same barrel that was fluted.

3. the barrel is lighter after machining removes the steel in those lengthwise grooves.

TRUE (sometimes) Depending on who machines the flutes, they can go from useful and lightening to cosmetic and a waste of time. Bushmaster flutes are deep, and my 14.5" HBAR is nearly the same weight as an M4 profile, except that the balance is more even, where as the M4 feels a little heavier out front (to me). The Olympic Arms fluted barrels I've seen (no direct experience with them) have been shallow grooves that definitely didn't take off enough metal to make a difference.

in conclusion, they said: " A fluted barrel will last longer, shoot straighter, and is considerably lighter than a standard heavy barrel. The accuracy gains would be most noticeable at longer distances or to the competition shooter."

While my fluted barrel certainly DID NOT suffer any negative effects in accuracy from fluting, I do not understand how fluting would make a barrel more accurate. Again, a fluted barrel that weighs 2.2lbs MIGHT be more accurate than a non-fluted barrel that weighted 2.2lbs, but fluting a barrel will NOT improve THAT barrel's accuracy.

I definitely don't know how it could make a barrel last longer.

For $50, it was worth it for me. I will continue to purchase fluted barrels, but for the weight savings with increased rigidity over a non-fluted barrel OF THE SAME WEIGHT.

 

[Harold Mayo]

I have a fluted barrel on my 16" Bushmaster carbine. I think that it was worth the extra $50 but I really only got it for appearance, I must admit. I don't have any illusions that it makes the barrel inherently "better" in any meaningful way.

 

[c_yeager]

the stiffness comment is absurdly misleading. It seems to me that the truth of the matter is that if you took an existing HBAR and fluted it, then end result would be weaker than the original. Not a good thing.

 

[Bartholomew Roberts]

Bushmaster would be better off if they added the caveat "of the same weight" to each of those statements. Onslaught hit the main points pretty well already; but just thought I would add:

1. increased radiational cooling of the barrel

As Onslaught noted, this is true; but the barrel will also have less mass and so it will heat up faster than an unfluted HBAR. Compared to a 2.2lb barrel, the fluted barrel will do nicely. Compared to the original 2.7lb HBAR it started as, the decreased mass will effectively negate the slightly increased radiational cooling.

A fluted barrel will last longer, shoot straighter, and is considerably lighter than a standard heavy barrel.

I believe Bushmaster is attempting to make the case that because the barrel is stiffer than a barrel of the same weight, it will have less barrel whip and be more accurate. Because it cools faster than a barrel of the same weight, it will last longer (heat and throat erosion go hand-in-hand).

However, a fluted HBAR will be less stiff and have no cooling advantage over an unfluted HBAR. It will be about half a pound lighter though.

 

[Chipperman]

It will heat up more quickly than an unfluted HBAR, but it will also cool down more quickly than an unfluted HBAR.

 

[Badger Arms]

Think of the barrel as a vessel for heat. The mass (use weight in this case) of the barrel determines how fast the heat is dissipated from the bore where it's generated. It also determines how much heat is dissipated. Since it heats up MUCH quicker than it cools down, the weight of a barrel is the major determining factor in heat control. Shooting 200 rounds full-auto through a fluted barrel will cause the barrel to heat to a higher temperature and therefore more distortion and damage to the bore than a heavier unfluted barrel. For semi-auto use, this factor is mitigated some and will probably go unnoticed unless you shoot target competition.

Now, on to the cooling effect. There is a phenomenon that plays a GIANT factor in the cooling of the barrel. This is the amount of air that circulates over the barrel. There is a 'dead space' of protected air between the flutes and immediately around the barrel. Unless you have a fan blowing over these flutes, the cooling advantage of the flutes is greatly diminished. I'm not a physicist, but the heat dissipation rate of an AR-15 barrel is NOT directly proportional to the surface area of said barrel. A 100% increase in surface area will NOT double the cooling rate. In fact, other factors contribute to cooling which you MIGHT not be aware of. Chrome-lining will decrease friction and therefore decrease slightly how much your barrel heats up. "Treating" the bore with a product like Tetra-lube will also decrease friction.

Finally, in spite of all the hype, misinformation, ignorance, and lies that exist about fluting, it comes down to a question of how much you are willing to spend. Spending $50 to save 8-12 ounces sounds like a great deal to me. The barrel will be stiffer and more potentially accurate than a standard taper barrel but without the weight penalty of the heavy barrel. No matter what you do, make DARN SURE that you get a chrome lined barrel for the sake of life expectancy and reliability. Fluted or no, chrome lining is a must.

 

[Badger Arms]

Happiness is a warm P7!

Hehehe, Yeah, but misery is a P7 that's heated up so much it burns your trigger finger when you are STUPID enough to lay it alongside the frame after a rapid session of reload drills!

 

[Chipperman]

Well, it's nice to have a hot gun in this weather.
Regular Brass Monkey weather we've got going on here right now.

 

[ajacobs]

http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm

This link goes into a whole bunch of detail I barrels and stiffness, and while I just read through it once I believe I am reading it right.

 

[ajacobs]

Darn, I miss Gale posting on the Firing line. I am certainly no expert. Here is another chart:

http://www.cctrap.com/~varmint/aflut.htm

If you look at the 5th and 7th one down or the 6th and 8th one down as pairs you notice that you are comparing 2 barrels of the same weight and same outside diameter. One fluted one not (although the barrel are of different legth). Notice that the barrel exit angle (comparable to MOA in External balistics) is less for the fluted which means stiffer.

Now if you look at the 1st and the 5th one you see two identical (same legth same ex. diameter) barrels one fluted one not, you will see that the fluted barrel is less stiff. These two are most comparable to a ar barrel prior to fluting and after fluting.

 

[zahc]

it looks cool

 

[Harry Tuttle]

the archive lives!

Gale McMillan
Senior Member


In the 1970s a bunch of target shooters were in our barrel shop and the subject of fluted barrels came up and the point of the discussion was that they wouldn't shoot well enough for target guns. That was the reason you never saw one on the line. After the discussion broke up I was talking about it with my brother and we decided to make a couple of barrels and flute them at a point in the manufacture that we thought it should be done. We made two and one was given to Harold Broughton of Big Springs TX and I put the other on my brothers gun. To make a long story short Harold won the NBRSA Nationals and Pat won the IBS Nationals and set two worlds records. I will say that while these two barrels were outstanding barrels it was in spite of being fluted and not because of it. After that everyone was fluting barrels and at any point from after they were made to before they were drilled. For my own point of view you couldn't' run fast enough to give me one that some one else had fluted. I once asked an other barrel maker why he fluted barrels and he answered . $2.00 a minute! That was what he made in fluting them.

http://www.thefiringline.com/forums/showthread.php?threadid=12953

 

[c_yeager]

Despite how much i dislike the misleading advertizing aurrounding fluted barrels Badger Arms makes a very good point. I always thought that fluting was all about saving weight. And for $50 its money well spent if you want a lightweight rifle that retains SOME of the characteristics of a regular HBAR. To my mind a fluted Heavy Barrel is better than an A2 profile barrel. SO if you are building a nice lightweight rifle to carry (the perfect role for the AR platform IMHO) then its probably money well spent. Plus, it does look pretty cool.

edited to add: the hands down best looking bbl i have ever seen in my life was on one of those custom 10/22s that you see from time to time. This one was a matte finished stainless fluted barrel with carbon fiber inlayed into the flutes to make it perfectly round. Might not work on an AR because of heat issues but it was gorgeous none the less.

 

[Nero Steptoe]

Yeager is 100% on this issue. Bushmaster's advertising isn't just misleading; it's false. The statement, "fluting a barrel causes that barrel to be stiffer" is false. Comparing that fluted barrel to a non-fluted barrel of the same weight is a false analogy.

 

[Badger Arms]

Comparing that fluted barrel to a non-fluted barrel of the same weight is a false analogy.

Not entirely. In fact, that's the point. One of Bushmaster's statements can be taken for gospel if you merely add the phrase, "of the same weight" to the end of them. Somebody said it earlier, I'll rewrite their statements with my addition in bold:

Fluting (machining lengthwise grooves into the outer surface of the barrel) increases the surface area of the barrel - thereby allowing increased radiational cooling of the barrel mass. This process also adds to the "stiffness" of the barrel when compared to another barrel of the same weight which enhances its accuracy. A third benefit of fluting is that the barrel is lighter after machining removes the steel in those lengthwise grooves. A fluted barrel will last longer, shoot straighter, and is considerably lighter than a standard heavy barrel. (well, this is a false statement and they should change it) The accuracy gains would be most noticeable at longer distances or to the competition shooter, but for only $50 additional for most Bushmaster barrels, many feel that the benefits of fluting are well worth the cost.

 

[Nero Steptoe]

Yep, it's a false analogy, although the statement about "of the same weight" is true.

Bushy's not making that comparison. They're clearly incorrectly alledging that paying the extra $50 to have their fluting job done will stiffen the barrel being fluted. That's wrong, and has nothing to do with comparisons of other barrels of the same weight.