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.


About the Author

Kilgore & Call
Richard Kilgore and Jake Call have been writing on and off for Military.com for many years now. You can reach them at BreachBangClear.com or follow them on Instagram at @breachbangclear or Tumblr at http://the-mad-duo.tumblr.com/.
  • 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.

  • burkefett

    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.

  • 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

    • burkefett

      My remark on ‘breathless hype’ was not directed at your article, I apologize for not being more specific. It was directed at the hype that tends to circle around process such as cryotreating barrels, fluting, and a few of the other process that have either no measurable merits, or significant tradeoffs for the advantages they bring. Your report was not what I’d describe as fanboyish, again, I apologize for the confusion. As I said, I don’t doubt that the Legion barrels are high quality and accurate, I just doubt the effectiveness and validity of some of their processes.

      • No offense taken here, and certainly no reason to apologize! I just wanted to make sure I didn’t come across that way. I want to make sure when you guys read my stuff I’m clear about what I have and/or favor (or dislike) vs. what I’m just ‘reporting on’. Opinions are like ******** and embarrassing relatives, I know you guys have better things to do than just read op-eds all day long. No worries, I appreciate the feedback from all of ya! (Even the ones who don’t like the way KU! is going.)

  • 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.

  • 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.

    • burkefett

      I don’t mean to seem like I’m being obstinate, but it is my understanding that the only method to achieve true polygonal rifling is, in fact, with the CHF process. Namely, the barrel blanks are hammered around a mandrel in the shape and diameter of the rifling using a pair of high-speed, opposed hammers. I’ve never heard of any other method for creating polygonal rifling, nor has a quick search shown me one. If there is another method, please feel free to enlighten me.

      Like I said in my original post, I have never once seen a single scrap of data that indicates a measurable increase in performance when cryogenic treating is used. This includes studies of the way barrels perform at the molecular level, commissioned by match-grade barrel makers. I don’t doubt that you heat treat the barrels, since using heat to relieve stress is a process that has existed for hundreds of years. However, I don’t believe that the cryogenic process has any effect.

      While I have no need for or interest in one of your barrels at the moment, I would be happy to purchase one at a later date, provided that they do in fact have true polygonal rifling and can be ordered in a standard, non-fluted profile. As I’ve said multiple times, I do not doubt that your barrels are accurate. I simply do not believe some of the technical processes you use, and your claim that you have produced poly-rifled barrels without using the cold-hammer forging process. In this instance, I am not, in fact, ‘confusing rifling with material manufacturing.’ Polygonal rifling is not cut, it is forged as a step in the barrel-making process.

      • Austin

        Lothar Walther uses polygonal rifling and Noveske uses their own variation of polygonal rifling and their barrels are button rifled not hammer forged. Are you saying that what these companies use is not a “true” polygonal barrel? It does not make sense to me that they would not be able to cut a polygonal rifled barrel. I am not attacking your statements, simply looking for a clarification since I have little knowledge of the rifling processes.

    • Eric

      Anytime you’re in san diego I would love to watch xm193 shoot sub moa at 100yrds. How far have you seen it holding under 1 moa, 200, 300, 400 yrds…?

      • If you would like to shoot one in your area contact the good people at Direct Action Solutions. They are one of our dealers. Also, the good folks over at Off the Grid Concepts are running our kit. We are maintaining sub MOA at 300 with out any issues. Here in Texas we have a couple dozen 3 Gunners running our barrels killing targets at 500 meters.

  • Lance

    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.

  • 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.

    • burkefett

      I am not an engineer, but please note that I never said that chf was the only method of making a barrel. I did say that it is my understanding that chf is the only way to make true polygonal riflng. It is also my understanding that while some types of cut rifling have profiles similar to poly rifling, they are not, in fact, true polygonal rifling. I have usually seen these particular types of rifling advertised as ‘cut rifling,’ not ‘polygonal rifling.’ I, along with the majority of the shooting community, associate the term “polygonal rifling’ as being rifling that is produced specifically during the chf process. We also tend to associate ‘cut rifling’ with rifling that is produced one groove at a time. In my opinion, your usage of the term ‘polygonal rifling,’ while it does represent the approximate profile of your barrels, is a slightly misleading way to refer to a cut-rifled process.

      I’m also curious about one of the other issues that I raised in my original post. What methods do you use to alleviate the issue of more rapid throat erosion and barrel wear during sustained fire with a lightweight or fluted barrel?

      • Since our barrels are 416R Stainless Steel and contains very little carbon throat erosion is not really an issue. Also we don’t cryo treat for accuracy we cryo treat for stress relief.

      • One thing that bothers me in the gun community is the narrow mindedness that some have towards something that is not from their preferred manufacturer, in their preferred caliber or in their preferred action. I have fired weapons ranging from the Red Ryder BB gun up to and including the main gun on an M1A1 Abrams Main Battle Tank. There are ways to ask questions to gain knowledge of something you are not familiar with, without calling out the “breathless hype” you perceived in the article. I have fired their weapons, even some of their prototype weapons, and can attest personally that they are superior to any AR style rifle I have fired to date. Be skeptical of all things, but be open to learning and evaluate them for yourself. There are far too many “experts” in the gun community that are negative to anything outside of their comfort zone and narrow focus.

        • Scout

          Here – Here! Monty, It’s not just in the “gun” community . It’s all over the Hobbyist world.. There was a post about this very subject sometime ago where it was openly pondered “Why are most people who work at /hang out in gun shops usually in the “know-it-all jerk” category? Or maybe it’s just an American thing.. I doubt the Swiss or maybe other shooting other cultures (How many are left?) have these types of silly scuffles about guns. A larger percentage of those populations are taught ‘how’ to think – not ‘what’ to think, and actually learn some basic science and mechanics in school. Americans sure may “love their guns” but our shooting population generally tends to know very little about how they work or how to use them well.

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

    • chuckytee

      Dang right Travis. And not some sissy .308,,,:) I wanna see that barrel treatment on a .338 or .50 cal.

    • Neal

      I’ll +1 that!

  • Mike Perry

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

  • slag

    As Fat ******* once said: “Do you think I’m sexthy?”

  • slag

    UGH bleepin filter, Austin Powers villain Fat Illegitimate-offspring

  • MarkM

    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.

    • Neal

      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.

    • jrexilius

      hehehe.. well said.

  • Scout

    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.

  • jrexilius

    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!

    • Skinny

      ^I’ll give a big +1 to everything said here.

  • Kevin

    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.

  • Jerry

    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.

    • 276 pedersen

      My understanding is that he fired the rifle that already had 7k rounds shot through it, not that he shot that number himself. Maybe I’m wrong, but that’s how it reads to me.

      • Agree 276 pederson. That’s how I read it also.

  • Glad ya like it, Lance.

  • Thanks fellas!

  • bbb

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

  • 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

  • 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.

    • I can’t find anyone on this page that even said “4 moa” besides you. So I am left with “HU?”. No one in this thread is saying that 4 moa is good enough.

      I am curious as to what MOA does Legion Firearms barrels hold at 300 vs 100.

  • Thanks Kevin.

  • 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: https://kitup.military.com/2012/03/hex-fluted-rifl
    Kit Up!

  • Robert Stokes

    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

  • 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.

  • 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.