07 May 2017

Is It Just Me

Or has the quality at The Firearm Blog dropped off precipitously of late?

I just got done reading that M4 barrels are inferior to M27 barrels because H&K uses chromoly-vanadium (CMV) steels and the M4 uses mere 4150.

That'd be well and good, except that CMV steels ARE 4150 steels.  And guess what the M4 uses?  CMV.

Let's just look what these numbers mean...

The 41 part means it's Chromium-Molybdenum (aka chromoly)  with Cr 0.50%, 0.80%, or 0.95%; Mo 0.12%, 0.20%, 0.25%, or 0.30%.  41xx is a very broad category.

The 50 part means that it's got near 0.50% carbon content.  (0.48 to 0.55% for Ordnance 4150).

So with max values of 0.95% Cr, 0.30% Mo and 0.55% C... 98.2% is something else!  Mostly iron.

MIL-B-11595E defines the composition of steels acceptable for use as barrels, it lists ORD 4150 ORD 4150 (Resulfurized) and Chrome-Moly-Vanadium; they are interchangeable to the DoD, by the way.

Where does CMV sit?  Carbon 0.41-0.49%, Manganese 0.60-0.90%, Phosphorus 0.040%, Sulfur 0.040%, Silicon 0.20-0.35%, Chromium 0.80-1.15%, Molybdenum 0.30-0.40% and Vanadium 0.20-0.30%.

Yup, that's 4150 steel, alright.  Just like a square is also a parallelogram and a rhombus.

Ordnance 4150 is Carbon 0.48-0.55%, Manganese 0.75-1.00%, Phosphorus 0.040%, Sulfur 0.040%, Silicon 0.20-0.35%, Chromium 0.80-1.10%, and Molybdenum 0.15-0.25%.

Ordnance 4150 (resulfurized) is Carbon 0.47-0.55%, Manganese 0.75-1.00%, Phosphorus 0.040%, Sulfur 0.05-0.09%, Silicon 0.20-0.35%, Chromium 0.80-1.15%, and Molybdenum 0.15-0.25%.

Yes, it can make a difference, but the point here is that both the M4 and M27 are using CMV steels when they ship from Colt and FN or H&K.

Bravo Company USA even destructively tested a Colt M4 barrel to confirm it too.

I think that I would rather know less than so much that is not so.


  1. FWIW: HK's supplier Aubert & Duval offers CMV alloys other than 4150.

    The following catalog is dedicated to firearms applications, but I understand that HK's specific barrel alloy is proprietary.


    Their defense catalog mentions a couple of additional CMV alloys for barrel applications.


    1. So H&K is making M27 barrels from a steel not approved by the milspec? Because all three approved steels are 4150 of some kind.

      Hang on, lemme get the popcorn!

      Ordnance 4150 is not generic 4150, nor is 4150 CMV although all are 4150 steels.

      I recall when Colt's CMV was a closely held trade secret and how difficult it was to get the chemical and mechanical properties to properly assess if it was worth the extra money. BCM did us a solid and destroyed a couple Colt barrels to answer that question.

  2. The size and color of the cupholders.......

  3. The USMC's IAR solicitation and testing process was kind of odd, especially in contrast to what you'd see from the US Army. Given the NDI nature of the IAR solicitation, it wouldn't surprise me that MARCORSYSCOM let HK submit whatever barrel steel it wanted. Of course, the test performance results would end up locking down the expectations for the production weapons.

    Is there even a Mil-Spec document for the M27 IAR, or is the USMC simply buying it as a service-peculiar, COTS item? The stainless steel barrels on the M40A6 and M45A1 aren't MIL-B-11595E compliant either. How many parts used in the previous MEU(SOC) pistol builds met the Mil-Spec for the M1911A1?


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