Hex Fluted rifle barrels: the whys and wherefores

There have been a lot of questions about the honeycomb “Hex Fluted” barrels built by Legion Firearms. A lot of people wonder if that’s strictly an aesthetic feature or even a gimmick, others challenge the idea that such construction actually strengthens or improves the barrel. I talked to Jamie Wehmeyer and Chris Reeves from Legion at length about these issues to try to illuminate things.

Note: in the interest of full disclosure, I will tell you up front I’ve had the opportunity to shoot a T&E model LF15D extensively and I was very impressed. It was certainly more accurate than I could exploit at my skill level and was over 7k rounds without cleaning when I had it. I do not own one.

Legion rifle barrels were R&Ded for 3 years before they went into production. They are not CHF (Cold Hammer Forged), they’re a 416R ordnance grade stainless steel. They’re chambered in 5.56mm NATO, cryogenic treated, 3-groove polygonal stress-relieved. Every  barrel is Cerakoted to prevent any rusting or external oxidation. There are a total of nearly 30 procedures and treatments that go into the barrels, though they understandably don’t go into detail about them. One obvious physical feature is Hex Fluting.

Essentially, the Hex Fluting design is based on the study of vibration—how it works, when it stops.

Wehmeyer clarifies, “I’m talking about the dissipation of an instance of vibratory motion. Call it motion, tremor, an oscillation, whatever term you prefer. It’s the underlying physics of it that are significant to the Hex Fluted barrel.”

Vibrations travel for longer distance through a curve than they will through a straight line or an angle. The so-called ‘honeycomb’ barrel capitalizes upon that.  Consider the difference between striking a steel drum vs. a steel box: a steel drum will continue to vibrate for as long as the shape can hold it, whereas a steel box will hold the vibration only to the closest corner.

Wehmeyer says, “The long term study of vibrations has yielded facts that the firearms industry has failed to acknowledge and capitalize upon for years. It’s not that the industry is dumb or naïve, it’s just that the different sciences frequently fail to cross-communicate enough to really affect each other in any productive manner.”

Legion guarantees their rifles will shoot sub MOA with cheap XM193 or PMC55 type ammunition. They’ve achieved one-hole groups with 3 rounds of 77 grain OTM (Mk262 Mod 1) 5.56mm at 100 yards, and every proficient shooter I’ve personally talked to has verified just how accurate they really are.

Another advantage to the Hex Fluted barrel is heat dissipation.

“Simple science fact,” Jamie says. “A greater surface area is going to yield greater heat dissipation given no disparity in material and relative mass. Also, strength and rigidity should not be measured by how much material an object contains but rather by its ability to retain its original form. [emphasis added] Our barrels are built the way they are for strength, heat dissipation and accuracy. The aesthetics of it are purely a byproduct.”

If you have any further questions, please advise and I will try to get an answer or will ask the Legion guys to watch the comment section so they can address them directly. Legion is also available on Facebook.


26 Comments on "Hex Fluted rifle barrels: the whys and wherefores"

  1. This is really interesting. I love the idea that someone is actually using modern science to study barrel harmonics. It seems in the past, even large manufacturers are building things by trial and error.

  2. I'm going to go with a hefty dose of skepticism here. For starters, how exactly are they achieving polygonal rifling without a cold hammer forging process? For another, every single bit of data I've studied on cryogenic treatments for barrels indicates that it has virtually no measurable effect on accuracy, despite the hype of internet fanboys. I'm also skeptical of the claims that these barrels will magically make crappy surplus ammo shoot into sub-MOA groups. I've seen and even shot a few sub-MOA groups with 55 and 62 grain surplus, but I'm inclined to believe that those are just a fluke of statistics – it doesn't matter how awesome your barrel is, it won't magically turn crappy ammo into match-grade ammo.

    I will grant that the circular fluting pattern probably does have a real effect on accuracy and barrel harmonics, but my primary concerns are two-fold: First, unless the barrels are stress-relieved by heat treating (not cold) after the fluting is machined, they will suffer problems such as wandering zero and poor accuracy during sustained fire. Since I have in fact heard that these are fairly accurate barrels, I'll assume that one of the 30 "secret processes" is, in fact, just regular old heat treating. The second thing I will note is that while yes, fluting will generally permit barrels to cool faster, it also allows them to heat up faster. Simply put, the more material that is removed from the barrel, the more you reduce its ability to act as a heat sink. The consequences of lightweight and fluted barrels under sustained fire are well-documented – namely, the tendency to heat more rapidly leads to an increase in throat erosion and barrel wear, adversely affecting accuracy.

    Like I said, while I'm sure that the unique fluting pattern may have some benefits for barrel harmonics, I'm pretty sure that the main driving force behind it is the really high chicks-dig-it factor. I don't doubt that these are exceptionally accurate barrels, but I prefer to go with more affordable barrels that are just as, if not more accurate. I, personally, prefer to purchase products that don't come with a hefty dose of breathless hype.

  3. Burkfett: I'll ask the Legion guys to respond to the issues you raise, and I agree about not wanting to jump on the average bandwagon, which sadly happens often in the industry. I'm not sure how you see 'breathless hype' in what I posted up there, though. That's certainly not what I was going for. If that came across as some sort of gushing fanboy type report, I either need change the way I write or I need to ask you to reread it dispassionately. In any case, I lack the qualifications to accurately respond to your points (well, intelligently anyway), but hopefully there will be other readers on here who can. DR

  4. I've had the opportunity to fire several Legion rifles (and their pistol) and have talked to Jamie and Chris quite a bit. I have learned much from them and know the passion they have for their product. I was impressed enough that I became a customer and a huge fan of them and their products.

  5. Birkefett,
    First of all I would like to thank you for taking the time to read Dave's article. Second of all we run demos out at Best of The West Shooting range anytime you would like to test our accuracy. I think you are confusing rifling with material manufacturing. Having a CHF barrel does not keep you from having any type of rifling like… That is only how the rifling is cut. You cut anything with polygonal rifling. Also cryogenic treating of a barrel IS heat treating. It is a more complex version of the treating since it is brought down to a super cold tempature then slowly brought up to high heat… And we do shoot sub MOA all day with cheap ammo. Buy a barrel, shoot it… If it doesn't shoot like we said feel free to send it back for a full refund and we will pay for shipping.

  6. Very interesting article thanks Mr. Reeder

    Id say down side and reason no military would do it is cost be expensive to have any new M-4 with this type barrel. But the heat dissipation is a great bonus and think for cops and competition tac shoots this would be a new awesome feature for a new AR. Honey comb is not only used for barrels but the F-15 and maybe the F-22 use this feature under its skin to dissipate heat when flying super sonic. Awesome idea to take this to guns as well.

  7. CHF is not the only way to make barrels or the rifling cut… And it is a cut. Not be insulting but I take it you are not a machinist or a engineer.

  8. Sounds good to me. Lets see how it cuts weight and improves performance in a long-range bolt gun!

  9. Mike Perry | March 16, 2012 at 1:37 pm |

    Black Hole Weaponry make 3 groove polygonal barrels and they are button rifled.

  10. As Fat ******* once said: "Do you think I'm sexthy?"

  11. UGH bleepin filter, Austin Powers villain Fat Illegitimate-offspring

  12. While we all are more familiar with polygonal rifling being used with CHF barrels, there's not much reason why a button can't do the same thing. It's basically a carbide tooth passed down the bore to create an internal profile. It doesn't have to have 4+ lands and grooves in it. And most of the other processes in making this barrel seem to be conventional, stress relieving is common, use of stainless, etc.

    What it boils down to is how the fluting is done – cast, CNC, or pressed/rolled. It was stated that the barrels are not CHF, which doesn't mean they couldn't be hot rolled and semi extruded. In terms of economic production, it's really which method gets the job done the cheapest, and doesn't create an expensive part to be discarded from initial barrel drilling defects. That puts CNC at the head of the pack in terms of least expensive for small lot production. If thousands a day were being made, then I'd go hot rolled to shape. That's not to say cast isn't being done – it's a common method used on the exotic tactical knife market, one the makers don't want to talk about. Cast has a lot of public misperception and doesn't market well.

    Aside from all that accounting and forming drudgery, the real issue is effective accuracy. In a combat weapon, all that has been needed on the battlefield is 2MOA, which nets a 10" group out to 500m. Frankly, the focus on ultra precision is a bit overdone – the average soldier simply doesn't need it, it's an long distance precision shooter issue, one that is hypermarketed in the industry a lot because testosterone influenced one-upmanship dominates most of the typical interaction between men.

    "I got one and you don't, that makes me "better" than you." Frankly, no, it doesn't, shooting thousands of rounds a month might make you a good marksman, it doesn't have anything to do with your net worth as a human. We get rated on how we treat others in life more highly. Something **** isn't demonstrating to any degree.

  13. For decades we've been using honeycomb structures in rockets and jets – where vibration and shock rule the day.. It's a wonder that this idea did not come earlier or maybe it did but manufacturing expense was too high. Working out an affordable manufacturing approach is what makes this a winner.

  14. Really good article and discussion. The back and forth really helps tease out more details and things to consider.

    Dave you're doin a great job with KitUp!

  15. Jamie, next time I see you guys, trigger time to T&E your rifle. Good points covered here.
    Looking forward to your next write up Dave.

  16. To the writer:
    In 7,000 rounds, you couldn't find the time to find a fixed benchrest and test that accuracy claim of 1MOA accuracy with non-match ammo? This "It shoots better than me" is a cop-out. Find a fixed rest and some sandbags.

  17. Glad ya like it, Lance.

  18. Honestly there's no one on the planet who is going to shoot 7,000 rounds and NOT find time to bench test it.

  19. Jerry; I'm sorry you think it was a cop-out, it certainly wasn't intended to be. The 7K rounds were the total rounds fired thru the rifle to that point. I didn't shoot them all. I wouldn't have had the time and I couldn't afford that many bullets anyway. Several shooters maintained records of what we shot and where for continuity purposes (like chain of evidence). As for it being a cop-out, what exactly are you looking for? I tell it like it is. I'm not a great shooter. I'm competent and proficient, but I can't hit out to the distances better shooters like my brother and some of you on here can do. Without optics I wouldn't even try to engage something out past the 300. I'd be endangering birds and gophers and any innocent livestock that might be in the area. I write as candidly as I can. The rifle shoots better than my skill level and I'm not going to claim otherwise. Please note I said "Legion guarantees their accuracy…", not that I claimed their accuracy (though I have no reason to doubt the assertion). I try very carefully to make no assertions beyond what I can support. I can no more argue the veracity of the hex fluted barrel advantages than I could explain how explosives propagate if I were to write about an EOD kit (other than the BOOM is fun to watch). I just advise the knowledge the best I can within the context of my (limited) training and experience. I am sorry you consider it a cop-out, however if you know a shooter or reviewer you think could accurately test the Legion rifle claims, you might consider trying to set it up. I'm not the only writer/reviewer who has contacted Legion to take their tools for a spin, so I know they're amenable to the idea.

    In any case, sorry you had issues with this article. Hopefully you enjoy others better. DR

  20. 4 MOA is not accurate enough for the average soldier/marine/airman… I have always hated that mindset and so have my cohorts. The riflemans job is not vague volume of fire but accurate target takedown. I'm not talking about a sniper rifle but POA/POI if you are aiming at a persons head ( because it is the only thing exposed) 4 inches from the center of the T zone can be a complete miss… Not accurate enough for me or the next person that needs to be In a time is life situation.

  21. That was in response to Neal March 17, 2012 at 10:31 am

    Agreed. How often is the soldier/sailor/marine/etc. going to have the nerves and ability to actually utilize that sub-MoA barrel in combat? 5.56 really isn’t an ideal cartridge for such long ranges to begin with.

    Read more: http://live-military-kitup.sites.thewpvalet.com/2012/03/hex-fluted-rifl
    Kit Up!

  22. Robert Stokes | April 12, 2012 at 5:23 pm |

    Hi Burkefett,
    Skepticism is appropriate, but I can't agree with your position that polygonal rifles barrels are cold hammer forged. I'm a competitive high power rifle shooter and own two rifles with polygonal rifled barrels, one is a PacNor barrel and one is a McMillan Tubb 2000 with a Schnieder barrel. Neither of these are cold hammer forged, both are button rifled. If you are not familiar with the Tubb 2000 here is a link to the specifications. http://www.mcmfamily.com/mcmillan-rifles-tactical

  23. My name is SSG Christopher Rance, Army sniper section leader out of Virginia. I have been running a T&E LF-15c for the past six months and I have put it through quite a bit of training. Just recently I used it up at Storm Mountain Training Center Urban Sniper course and I had no issues getting standard Army issue M855 and MK 262 Mod 1 ammo out to 650 yards. It ran great in stress shoot scenarios and hostage taker "headshot engagement" scenarios. I would run this rifle over in the Stan in a heart beat. Its a damn fine battle rifle that delivers on its promise of being accurate. If your near Fort Myer, come out and shoot it and see for yourself. My door is always open.

  24. Burkefett,

    I know that I'm like, almost a year late to this party, but thought I'd throw in my understanding of poylgonal rifling vs. polygonal bore, which might clear up your confusion. So… the only way to get a true polygonal bore, like the kind found on H&K's famed PSG-1 rifles, is to use a CHF process, where the barrel is formed around a mandrel and the twisted polygonal shape of the bore itself provides the "rifling" for the barrel, with no lands or grooves used whatsoever. That constitutes a true polygonal bore and can only be achieved through CHF, as far as I know.

    Then there is what has become to be known as polygonal rifling, but also goes by names like 5R rifling, and is basically rifling that is cut into a barrel where the land's sides are sloped rather than cut at 90-degree angles, and where the lands are always opposite to a groove rather than opposite to another land. This kind of polygonal rifling (as opposed to a true polygonal bore) can be cut into a barrel using any of the traditional methods for producing rifling. Polygonal rifling is supposed to have some (or many) of the same benefits of a true polygonal bore.

    Hope this helps.

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