Can a Modern Pencil Barrel Take the Heat? InRange TV Puts Faxon’s Stress Relieved Barrels to the Test

The traditional wisdom goes: Lightweight or “pencil” profile barrels can shoot great – just so long as you don’t get them hot. After a mag or two of heat is dumped into your lightweight build, your point of impact (POI) will probably shift by several minutes of angle. If you don’t like it, then you’d better go for a thicker profile or learn your holdovers, because that’s just a fact of life with pencil-thin tubes.

Or is it?

Faxon Firearms claims their stress relief process frees thin profile barrels from the uneven stresses that cause POIs to shift when a barrel is put under thermal load. Ian and Karl of InRange TV chose Faxon barrels for “What Would Stoner Do?” project to reduce the weight of the modern fighting AR-15, on the basis that if Faxon’s claims were true, it would allow them to reduce the weight of one of the rifle’s heaviest components – it’s barrel – without compromising its rapid-fire performance. Yesterday, the duo published their test of the WWSD rifles and their Faxon barrels on YouTube, and the results were extremely surprising:

Faxon, it seems, knows a thing or two about barrels. Ian and Karl’s test proved out Faxon’s claims, with the WWSD rifles experiencing significantly less thermal shift (possibly none) than the legacy SP-1’s M16A1 profile barrel. Truth be told, I was extremely surprised, since thermal shift is something that has plagued lightweight barrels for decades. Thermal shift during extended or rapid strings of fire is the primary reason why heavier barrel contours are now favored for military applications, for example (the other, less important reason is raw thermal load – barrels will eventually give out under too much heat, and heavier barrels have more mass to absorb heat than light ones). A lighter barrel that maintains its POI during and after rapid fire would potentially allow a significant reduction in weapon weight, to the tune of half a pound.

With the Battle of Wanat and experiments demonstrating the structural failure of lightweight barrels under extreme heat loads still fresh in the minds of many, the likelihood that the next infantry rifle will have a super-thin pencil profile barrel is probably fairly thin. For the civilian shooter looking for a lighter weapon, though, pencil barrels that do not experience thermal POI shift should be extremely interesting.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • ExMachina1

    They not only demonstrate that modern stress relief appears to works, but also that shorter barrels might be more resistant to whatever warping effects might remain.

    • Black Dots

      I’ve been telling my wife that for years, but she remains unconvinced.

      • ExMachina1

        Maybe all you need is some stress relief

        • Rick O’Shay

          I hear they’ve got a glove for that now.

      • Anonymoose might be able to help you. :^)

      • GaryOlson

        Cryo treatment for the barrel should give more consistent results

        • Martin T

          True but then you run into diminishing returns…

    • Rnasser Rnasser

      The rigidity of a cantilever beam of constant section decreases with the 4th power of lenght…
      But you cannot beat the fact that shorter barrels lose a lot of velocity.

  • Drew Coleman

    An interesting thought – would being chrome lined (most military barrels) affect the stress relieving process vs being nitrided like the Faxon ones?

    • Rnasser Rnasser


    • It is primarily the the manufacturing methods that affect thermal shift versus the final coatings/treatments.

      • Black Dots

        Genuinely curious: are you able to share any of those manufacturing methods, or is that the secret sauce?

        • Rnasser Rnasser

          Probably Faxon just takes the time and care to make a high quality concentric barrel, and then stress relieves it properly. Not “secret” but well done.

        • BrandonAKsALot

          Stress relieving most steels is essentially the same process. Steel is a very interesting and unique metal if you really read into it.

  • 5 round groups, eyeballing the group center, and using blaster ammo, no group analytical software…

    The data derived from this test is inconclusive. It provides very little evidence of Faxon’s claims. This is a McDonald’s drive through test.

    • So, how do you account for the SP-1’s shift?

      • You cant even compare the sp1 barrel to the modern barrels tested as that old SP1 barrel isn’t even freefloated. The pressure from the rest would shift POI on any hot barrel if it was not free floated. He also used irons instead of a magnified optic.

        To test that SP1 barrel, free float it and and use the same optic used in the prior test, and switch to match ammo at the bare minimum.

        Also Karls “shrinking 4 round group” could be explained by pure random chance. Four rounds, since he discounted the flyer, is even less significant and less representative of group center.

        The test is a wash in my opinion.

        • ExMachina1

          I agree that the SP1’s lack of a free float barrel makes this an apples-to-pears kind of a test. Faxon has my attention but I’m not convinced

        • 40mmCattleDog

          This was my thought exactly. I love inrangetv but this wasnt exactly the best video ive seen of theres. I think ill stick with the CHF FN machine gun steel barrels.

        • “You cant even compare the sp1 barrel to the modern barrels tested as that old SP1 barrel isn’t even freefloated.”

          You’re right, but that probably does not matter very much since they are not using a sling, but a rest instead.

          “The pressure from the rest would shift POI on any hot barrel if it was not free floated.”

          Maybe. M16A1s are pretty damn light for the amount of POI shift they are seeing, and it’s not in the right direction, either. Plus we see POI shift down, left, right, etc in guns all the time when they get hot. So this does appear to be an issue, and the test of two Faxon barrels appears to indicate they suffer from this less.

          “He also used irons instead of a magnified optic.”

          Um, that would alleviate the problem, not exacerbate it.

          “To test that SP1 barrel, free float it and and use the same optic used in the prior test, and switch to match ammo at the bare minimum.”

          You could do that, sure. It was obviously not something Ian and Karl could do easily. What’s more interesting is that we see very little shift with the Faxon barrels, where I would expect to see more, just based on my experience.

          “Also Karls “shrinking 4 round group” could be explained by pure random chance. Four rounds, since he discounted the flyer, is even less significant and less representative of group center.”

          I don’t think anyone actually claimed the barrels got more accurate as they got hotter. Pretty sure Karl says that was just random chance.

          “The test is a wash in my opinion.”

          Do you own! I’d be happy to report about it!

          • I still have to disagree with your assessment. The test has too many variables.

            I suppose i could ask Faxon for a barrel for T&E, but i wouldnt be able to touch it until 2018. I am currently working with two other companies and their barrels.

            Thanks for the invite, but im too wrapped up at the moment.

          • Martin T

            The comparison has multiple inconsistencies. They would have been better served just showing performance of their barrel under heat stress WITHOUT a comparison to a product that was mechanically inferior from the start.
            Most people with interest in these kind of specs will see right through this what it is… and it makes the company look loke they are taking a cheap shot at marketing.

  • Emfourty Gasmask

    I use a pencil barrel AR in the local 2 gun competition here, and I’ve never noticed any dramatic POI shift compared to my older Heavy barrel AR. Granted I’m not anywhere near professional so, take that as you will, but I do some pretty rapid strings of shooting and the rifle does fine.

  • john huscio

    Sionics makes chrome lined pencil barrels that are, at least anecdotally, as accurate as nitrided barrels

    • Bradley

      What’s the point though? Nitriding is still more corrosion and wear resistant

  • James Wilson

    Faxon Nathan
    Nathaniel F
    …hmmm 😉

    • Faxon Nathan is TFB’s Nathan S.

      • Who, I should clarify, is not me.

        I mean, for a start, my name isn’t “Nathan”.

        • Moreover, your first name is spelled differently than his: Nathaniel versus Nathanial.

        • iksnilol

          But we’ve never seen you two in the same room.

          • No. The world tends to meltdown when we are in the same room. Our combined brilliance melts the minds of inferiors. 😉

          • iksnilol

            Or you’ve got a scary twin personality thing that’s bad at cover identities going on?

  • Seth Hill

    I see Faxon has their Gunner profile with the 5R rifling in the Match series. Have been waiting for that combo, looks like it is time to place my order.

  • Joshua

    I have a post coming that’s being moderated…

  • Mrninjatoes

    Why didn’t they use a legit long range scope?

  • James Wilson

    This is why I have yet to buy a Faxon barrel. It seems like they put out a good quality barrel at an acceptable price, but they’re overgassed (I get it. Wolf ammo.), just “meh” accuracy (1.5-2moa with match ammo at .75-1moa), and reportedly excellent customer service.

    I say reportedly because the one time I contacted them with a question regarding when a product would be released, I never got an answer (James Wilson is not my real name. Simply a reference to a largely forgotten founding father.)

    I look forward to seeing tests (biased and unbiased. Hey, guntubers gots to make money. It’s all good.) of their “match” line.

    When a flame fluted 6.5 grendel barrel comes out, I’ll buy it. I have zero doubt it will work for my piggy hunting needs and look awesome doing it.

  • “When their ARAK failed, everyone said it was perfect.”

    You mean like this?

    • Joshua

      Yeah those comments from Nathan are what i generally see from them regarding their products failing.

      You should have seen them acting like it was normal for those full auto tests between CL and Melonite to be so overgassed and have so many Stoppages…just normal operation…nothing to see here.

  • Jim_Macklin

    Traditional barrel are not straight when manufactured. After boring, and rifling and outside turning barrels are mechanically straightened using old technology dating to WWI.
    Modern barrels are manufactured straight and stress relived, perhaps with heat and then cryogenics.
    When barrel is bent back to appear straight it will relax the stress when it gets hot, say 500°F it is still not hot enough to normalize which needs closer to 1200-1500° and then slow cooling over a period of several hours.

    • Methods have changed a bit in the last few dacades. Mechanical straightening is not common to rifle barrels in modern manufacturing due to huge gains in gundrilling accuracy and tolerance control.

    • Corey R. Wardrop

      When (generally) did mechanical straightening phase out?

  • Geoff Timm

    But, what about synthetic ruby barrels? Geoff Who is a very curious fellow.

  • iksnilol

    I worry not if it will take the heat. Just how much will the rounds disperse after heating in a pencil and standard barrel.

  • Joshua- I sincerely appreciate your thoughts. Love to continue the conversation in detail.

    On the full auto test, we went into a lot of detail with MrGunsNGear on the testing and even did a full debrief video with him where we lay it all out.

    We wanted to show the barrels in detail after the test and committed to it. FedExs loss of those became a PR nightmare of epic proportions. Instead, we had to settle for observations, which was far from ideal.

    My direct email is

    Look forward to hearing from you.

    • uisconfruzed

      Excellent reponse

  • Corey R. Wardrop

    “Stoner never thought his rifles should be in 5.56.”

    Not really true. This was his initial assessment, but he was converted to a SCHV proponent.

  • Don_R_P

    Has anyone thought about adding on a heat sink? JPrifles sells the “Thermal Dissipator” which is a heat sink for your barrel.

  • JamesDrouin

    The difference between an actual “test” and what these guys did is analogous to the difference between an elephant and an elephant’s footprint.

  • Chuck Doan

    For civilian application, what is the rate of fire does one really need? Pencil barrel is fine. BTW the Tavor has pencil barrel.

  • Budi Utomo

    I’d say no pencil barrel will survive because all manufacturers for a carbine basis SMG use heavy barrel. Possible- if it was titanium or Rhodium-nickel steel.