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Thread: Why is 4150 steel better?

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    Why is 4150 steel better?

    I come from an Aviation Maintenance background, so I understand the 41xx series of steels to a certain extent. I have heard quite a bit about the desireability of 4150 CMV has the "best" steel for AR barrels, and I'm wondering why that is.

    Some of the explanations I've heard here, and on other internet forums is not correct. While 4150 has a higher hardening potential, due to the greater content of carbon, it also has a higher "brittleness" potential, again, due to the greater content of carbon. Which means it is less "malleable" than 4140.

    So 4150 is not "tougher" than 4140, with "toughness" being the combination of hardness and malleability.

    So, what is it about 4150 that makes it a superior barrel metal, especially with a hard-chromed bore? I admit to being unfamiliar about what stresses are put on a barrel, understand that a certain need for "hardness" is necessary. (One cannot prescribe Viagra to an AR15.) In other words, how is 4150 superior to 4140 with a hard chromed bore in dealing with the stresses produced by shooting?

    Thanks!

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    I'm not a mettalurgist, nor have I played one on TV or stayed in a Holiday Inn Express.

    I don't know why it's used and I'm sure there is a reason why Colt, FN and LMT and others use it, I'm sure they would use 4140 if 4140 was superior since 4140 is cheaper.

    I found this when researching the differences.

    4140

    * Carbon range: .38/.43%.
    * Otherwise there is little difference between 4140 and 4150.
    * However, 4150 is selected when slightly higher mechanical properties are required.
    * Golf club shafts, badminton racquet handles, tamping rods, tufting needles, drill-shank tubing, key sockets, electrical connectors, and hand tools are typical applications.

    4150

    * Carbon range: .48/.55%
    * Otherwise there is little difference between 4140 and 4150.
    * However, 4150 is selected when slightly higher mechanical properties are required.
    * Golf club shafts, badminton racquet handles, tamping rods, tufting needles, drill-shank tubing, key sockets, electrical connectors, and hand tools are typical applications.

    This sounds kind of interesting too:

    http://www.springerlink.com/content/f7j456455466j063/
    FFL/SOT armorer

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    this could go on for ever,I for 1 don't have the resorces to do the testing that the G has done (who does) but they have determined it to be better for heat and durability. so they spec it ,if they are willing to spend your tax dollars on it than that's good enough for me . the prime reason the folks who use 4140 is it is cheaper .the best always cost more .the folks who will settle for less tell you it is just as good ,I often wonder how much real life testing they have done to reach that conclusion .
    WHO ME ? ---- A government big enough to
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    Quote Originally Posted by GONIF View Post
    the prime reason the folks who use 4140 is it is cheaper .the best always cost more .the folks who will settle for less tell you it is just as good ,I often wonder how much real life testing they have done to reach that conclusion .
    I've seen the "just as good" argument, and it seems overly simplified on both sides.

    My understanding on why 4150 is preferred over 4140 for military use is that, in simplified terms, it's better for long-term, hard usage. Less prone to fatigue and failure for burst fire and full-auto fire. If my understanding is reasonably correct, 4150 would be better in a military application, and "just as good" would not be "just as good."

    However, civilian usage is highly unlikely to push the performance envelope the way military usage does. I doubt even law enforcement usage would replicate day-in, day-out military usage. Thus, for civilian usage, you would find no differences in performance between 4150 v. 4140. So does that mean 4140 would be "just as good"? Not for me. For me, a civilian, 4140 would be better not in performance terms but in cost-benefit terms. If for my usage I have a choice between two types of barrel steel, and neither one offers me any measurable benefit over the other, the best choice is the least expensive of the two.

    As for real-life testing, I think that's basically been done by years and years of real-life usage in the civilian world. I have never yet found a single instance of a barrel failure in civilian usage that was attributable to using 4140 steel rather than 4150 steel.

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    So the" I think" test is your hall mark test ? maybe someone should tell Colt,Bushmaster,and LMT they are wasteing money . the big guys pay so little for the upgraded steel it is a non issue . some folks need ,want,deserve and get the best some don't. I for one a'm not going to tell anyone what is good enough for them ,I deserve the best and that ain't good enough . life is short why settle ? Cheap scotch will get you drunk just as fast as12 year old Single Malt will ,but it won't make you smile after each sip . I realy a'm not trying to bust you chops ,but best is best and for most of the things we buy it may be a moot point an AR is in fact a weapon you may some day have to bet your life on so get the real deal proven to be superior barrel .just MHO. YMMV
    WHO ME ? ---- A government big enough to
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    Quote Originally Posted by GONIF View Post
    So the" I think" test is your hall mark test ? maybe someone should tell Colt,Bushmaster,and LMT they are wasteing money . the big guys pay so little for the upgraded steel it is a non issue . some folks need ,want,deserve and get the best some don't. I for one a'm not going to tell anyone what is good enough for them ,I deserve the best and that ain't good enough . life is short why settle ? Cheap scotch will get you drunk just as fast as12 year old Single Malt will ,but it won't make you smile after each sip . I realy a'm not trying to bust you chops ,but best is best and for most of the things we buy it may be a moot point an AR is in fact a weapon you may some day have to bet your life on so get the real deal proven to be superior barrel .just MHO. YMMV
    So, in other words, you know nothing of the properties of different steels and why they are selected based on the intended use. You just do the .mil monkey-see monkey-do.

    At least Whytep38 has thought the question through using correct information. You may disagree with him, but at least put some thought into an answer that everyone is going to see.

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    Anyone remember seeing the chart of analyzed barrel steel parameters between some different barrels that Paul of BCM had?

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    No I did not say that I didn't read all the spec's and maybe even understand the tec reasons ,what I said is I do not have the ability to do the tests the G has .
    WHO ME ? ---- A government big enough to
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    Quote Originally Posted by GONIF View Post

    ...if [government agencies] are willing to spend your tax dollars on it than that's good enough for me.
    Now THAT'S a scary belief!

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    Quote Originally Posted by 120mm View Post
    So, what is it about 4150 that makes it a superior barrel metal, especially with a hard-chromed bore?
    I'm not sure that the metallurgy tells us the whole story. In short the barrel must sustain X rounds before deflecting or sagging under sustained fire...

    4150 allows for sustained fire from an M4 or M16 with deflection that does not endanger the soldier.

    In short, the NOTICEABLE difference in 4140 vs. 4150 will come at the outer limits of either barrel.

    In other words, there is a very specific requirement to be met and 4150 does it.

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    I'm also speaking off-line with a bench-rest shooter, who also builds AR-15 rifles, and he seems to think that the additional hardness helps with the rate at which the muzzle "bells out" as higher round counts/rates of round counts increases. This is more prominent with threaded barrels than unthreaded barrels, btw.

    That appears to make sense on the surface.

    I know from working on aviation steels, that it is much tougher to screw up the lower numbered steels. 4130 is the easiest to work on, while 4140 and 4150 become harder to work without making them overly brittle or wearing out your tools. In other words, if you don't have perfect quality control, 4140 has a better chance of turning out "tougher" than 4150. The additional hardness potential of 4150 requires a higher QC, in other words.

    I seem to recall something about heat dissipation superiority of 4150 over 4140.

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    Quote Originally Posted by GONIF View Post
    So the" I think" test is your hall mark test ? maybe someone should tell Colt,Bushmaster,and LMT they are wasteing money . the big guys pay so little for the upgraded steel it is a non issue . some folks need ,want,deserve and get the best some don't. I for one a'm not going to tell anyone what is good enough for them ,I deserve the best and that ain't good enough . life is short why settle ? Cheap scotch will get you drunk just as fast as12 year old Single Malt will ,but it won't make you smile after each sip . I realy a'm not trying to bust you chops ,but best is best and for most of the things we buy it may be a moot point an AR is in fact a weapon you may some day have to bet your life on so get the real deal proven to be superior barrel .just MHO. YMMV
    I wrote "I think" because I am 1) admitting that, not being an expert in some things such as metallurgy, I must rely on the expertise of others, and 2) although I have never once found any barrel failure in civilian usage of 4140 v. 4150, there may be a case of it happening. I still have not heard of such a failure, nor have you provided any such information.

    Your response contains its own "I think" on your part. You "think" the military is using the very best steel out there for its barrels. Do you know that for a fact? Although the military has performed numerous and expensive studies of various materials, every decision is a compromise. One need only look at the history behind the M-16's development within the military to see that. Based on my experience in the military, which includes 2000 flight hours with the Navy, I can assure you that there are other times when the military makes compromises. For example, my issued MB-4 flight computer (a type of aviation slide rule for solving navigational problems) had letters and numbers painted on the metal surfaces. Those letters and numbers soon wore off, so I (like every other nav I worked with) bought a civilian version in which the letters and numbers were etched into the surface. The military version was a compromise. The civilian version was a compromise. In my case, the civilian compromise was the better of the two.

    Based on my experience in the military, my experience in production management, and my common sense, I believe the military is using the best compromise for its purposes when it demands 4150 steel for its barrels. I also believe that there is probably an absolute best, no-compromise steel for military purposes that the military would not choose because it would be far more expensive than the 4150 that sufficiently does the job. I also believe that the military's purposes do not perfectly mirror civilian purposes, and that the differences warrant thoughtful consideration rather than blind adherence.

    Your scotch analogy is flawed because it compares two vastly unequal choices. A better analogy is the difference between Napa Valley wines and Sonoma County wines. Each region produces high-quality, flavorful products, but they satisfy different flavor expectations for the drinker.

    But back to the point: If you have any proof that my 4140 barrel is going to fail in my time of need simply because it's not 4150 steel, please provide that proof. Otherwise, you're preferring 4150 simply because "you think" it's better for civilian usage.

    P.S. If you think the big guys (or anyone else) will pay even a little bit more for their steel but not pass that additional cost along to consumers, so that it becomes a non-issue, then you and I will have to agree to disagree.
    Last edited by Whytep38; 09-02-07 at 11:01. Reason: P.S. Added.

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    It was explained to me by someone with a PEng in something relating to this - that the metal maintained its strength better when hot. Creating a safer barrel - and one with a greater longevity.
    It was in relation to accessory mounting and the like - so I cannot offer anything else other than it will droop less etc.
    *I'm a knuckledragger so take this with a grain of salt, all of the conversation was in relation to the droop and subsequnt bolt sheer when weight is applied onto the barrel...
    Last edited by KevinB; 09-02-07 at 10:50.
    Kevin S. Boland

    Director, Combat Systems Development and Support
    Knight's Armament Company
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    1(321)607-9956
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    www.knightarmco.com
    *note I am a satellite office in Northern Virginia

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    Quote Originally Posted by KevinB View Post
    It was explained to me by someone with a PEng in something relating to this - that the metal maintained its strength better when hot. Creating a safer barrel - and one with a greater longevity.
    It was in relation to accessory mounting and the like - so I cannot offer anything else other than it will droop less etc.
    *I'm a knuckledragger so take this with a grain of salt, all of the conversation was in relation to the droop and subsequnt bolt sheer when weight is applied onto the barrel...
    Kevin,

    Given that it's "heat related", did your PEng indicate whether or not semi-auto fire would be enough to stress the steel and get to the heat threshold where 4150 makes a difference? I've heard the arguments that 4150 is needed only for FA fire, just wondering if that statement has any merit or if there's a known rate of fire where 4140 enters the not so desirable" zone.

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    Well it was in relation to 4150 versus other compositions.
    And the forces and heat when items like a rail, grip, PEQ and light are added.
    It was a military related issue - so the modelling and testing involved a high rate of fire.

    I was more hoping someone with some metalurgical background would chime in.
    Kevin S. Boland

    Director, Combat Systems Development and Support
    Knight's Armament Company
    701 Columbia Blvd.
    Titusville, Fl 32780
    1(321)607-9956
    kboland@knightarmco.com
    www.knightarmco.com
    *note I am a satellite office in Northern Virginia

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    Note should be made that the steel quoted by the OP was 4150 CMV An examination of the chemical analysis of 4150 per AISI specifications shows that this steel is indeed an easier hardening grade but also that vanadium is not present in the alloy. The confusion in terms of barrel steel is that the correct alloy is not 4150 rather a modified vanadium bearing grade per mil specification. The presence of vanadium acts to slow the response of the steel to heat treatment but also as a grain refiner. This promotes excellent ductilty and a high Kic value.

    With this noted buyers should beware that they are not getting what they believe is a premuim barrel steel when in fact the vendor has simply used plain AISI 4150 in place of 4140.

    Bill Alexander

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    This subject always get's heated,and never has a answer everyone is happy with. IMHO no one can afford to do the extensive testing that our Gov has done on this subject and as such I will defer to them on this. I have had first hand experience with both and have not had a failure with ether. my research on this subject has led me to belive the 4150 is superior for a chrome lined AR15/M16 barrel . as far as believeing our government ,I can't help you there .you aren't even going to get me started on that . life is strange,just the other day I saw on TV news that mother Taresa (spelling) lost her faith at some point B4 she died . kinda makes you wonder how she came to that .
    WHO ME ? ---- A government big enough to
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    Quote Originally Posted by Bill Alexander View Post
    Note should be made that the steel quoted by the OP was 4150 CMV An examination of the chemical analysis of 4150 per AISI specifications shows that this steel is indeed an easier hardening grade but also that vanadium is not present in the alloy. The confusion in terms of barrel steel is that the correct alloy is not 4150 rather a modified vanadium bearing grade per mil specification. The presence of vanadium acts to slow the response of the steel to heat treatment but also as a grain refiner. This promotes excellent ductilty and a high Kic value.

    With this noted buyers should beware that they are not getting what they believe is a premuim barrel steel when in fact the vendor has simply used plain AISI 4150 in place of 4140.

    Bill Alexander
    Thanks Bill I was hoping you would chime in on this one.
    FFL/SOT armorer

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    Even with the information provided by Bill, I don't see an easy answer to the OP's question about why 4150 is better. The answer isn't easy because you must consider the entire context. The government's testing was performed with specific military, not civilian, criteria in mind. To say "best is best" without taking into account any other considerations is an over-simplification.

    I don't know which of the weapons listed below does or does not use modified vanadium 4150 barrel steel, but I suspect at least one does not:

    M1
    AK-47
    M2
    Abrahms tank

    Using the simple "best is best" approach, if any of the above weapons use something other than modified vanadium 4150, they would not be using the best barrel steel. Thus, anyone betting his life on such a weapon would not get the real deal. And yet I've never heard of any of the above weapons being faulted for their barrel steel. I suspect that's because the "best is best" approach is so highly dependent on so many factors that there is no universal "best is best" for all applications.

    If people feel better about choosing 4150 (whether modified vanadium or not) over 4140, that's their choice. One should choose what best fits one's comfort zone. But scare-mongering folks about the issue without any proof is a different thing.

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    Quote Originally Posted by Whytep38 View Post


    If people feel better about choosing 4150 (whether modified vanadium or not) over 4140, that's their choice. One should choose what best fits one's comfort zone. But scare-mongering folks about the issue without any proof is a different thing.
    Who's scare-mongering here?

    I think there's VERY little statistical difference too. For the people that shoot 500 or less rounds a year the difference is nill.

    Last month I shot over 500 rounds through my 3gun rifle, and 2 others (400 though my LMT and 100 through my Colt) and that was a fairly light month.
    FFL/SOT armorer

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