The More You Know: Cold Hammer Forging (CHF)

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The Cold Hammer Forged marking ‘CHF’ is stamped into millions of rifle barrels around the world. And while it’s not the only way to make a barrel, for AR15 patterned rifles it is likely to be the most common*. But what exactly does that CHF mark mean? Let’s take a brief look at one part of a type of barrel-making process.

* Button rifling is the most common AR barrel manufacturing process.

Cold:

Ok, not exactly cold – by ‘cold’ we mean ‘not hot’. The CHF process takes place at room temperature, and even though the metal will warm up under pressure and work, it’s nothing compared to a temperatures used in other forging processes. For example, hot forging will usually take place at 80% of the metal’s melting temperature (red hot).

Hammer:

Hopefully you aren’t picturing a framing hammer and a 10 penny nail. The hammers used in the CHF process are heavy pieces of metal that are shaped and angled to pound the barrel blanks into shape (see below).

Forging:

Not only does the forging process shape the barrel, but it strengthens it as well. The repeated blows by the hammers align the molecular “grain” within the metal, increasing rigidity and strength.

The last, but important, part is that a mandrel and reamer are used to form the chamber, bore and rifling as the hammers pummel and elongate the barrel.

A diagram of how the hammers contact the blank – http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000200024

Credit: scielo.br

Credit: scielo.br

Tensile strength increases with CHF processes (32CDV 13 steel used as an example).

Credit Scieno.br

Credit: Scielo.br

CHF a shotgun barrel:

Total Materia – http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=277

The cold forming process is similar to the cold heading process, however, the process uses vertical presses instead of horizontal cold heading machines. The cold forming process is also volume specific and the process uses dies and punches to convert a specific “slug” or blank of a given volume into a finished intricately shaped part of the exact same volume. The cold forming process generally compliments the cold heading process by adding more intricate shapes to the cold headed blank.

Cold Hammer Forging machine:

CHF

Credit: SandHammerForging.com

Cold forging is a reliable and cost efficient process. The main advantages are the following:

  • savings in material and final machining,
  • high productivity,
  • excellent dimensional accuracy and surface quality of cold extruded parts,
  • improvement of mechanical properties of extruded parts
  • favorable crystal grain flow increases toughness.

RifleShooterMag.com – http://www.rifleshootermag.com/gunsmithing/gunsmithing_rsgunsmith1/#ixzz4NCoGP3fg

All About Barrels: 

The fact that hammer forging works is attested to by the fact that most of the major firearms manufacturers use it-Remington, Winchester, Ruger, Sako and Steyr, to name a few. Indeed, Savage may be the only major company that uses button rifling. Obviously, either method is capable of prod-ucing an accurate barrel.

One would think that [hammer forging], especially, would put all kinds of strain on a barrel. I mean, we’re taking about taking a nearly 2-inch-diameter bar of steel about 12 inches long with a hole through its center, and by hammering the living hell out of it, elongate it into a 24-inch-long tube having a muzzle diameter less than one-third of what it was originally. I mean, we’re talking major stress and realignment of the steel’s molecular structure here; that’s why the stress-relieving process is so critical.

Daniel Defense talks about Barrel making:

Want to CHF your own barrel blanks? Good luck – the CHF process requires 50 tons of pressure per hammer. Machines that can pull off that kind of force dont come cheap. That ‘The More You Know’ about Cold Hammer Forging.

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Pete

LE – Science – OSINT.
On a mission to make all of my guns as quiet as possible.
Pete.M@staff.thefirearmblog.com


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  • Anonymoose

    From the Beretta video: “F— you, bird! DIE DIE DIE DIE!”

  • Sasquatch

    Cool good to know.

  • AHill

    Wasn’t aware nonhuman primates were absolutely necessary to the process… I’ve always read they use a MANDREL not a MANDRILL. Maybe the people you talked to use a new process?

    • Edeco

      Yep, aggressive ones with blue snouts and red butts. Lower end manufacturers use marmosets and zamak alloy.

      • Bill

        No lemurs?

        • AHill

          Lemurs don’t respond well to chroming or nitriding process. They keep dying from the toxic fumes and the Workman’s Comp payments are already…murder….

    • Pete – TFB Writer

      No, no, no. You have it all wrong. My drill identifies as a man. Classic drill humor. You’re welcome.

      • AHill

        Then I suppose you should have some transdrill-friendly bathrooms installed… At TFBs expense of course.

        • Mystick

          The difference is that one has chuck and the other a collet.

          • Pontificant

            I once had a collie named Chuck. Does that count?

    • What you started has turned into a work of art. This is a great online community.

      • AHill

        Why thank you! I cannot take all the credit but I am certainly willing to take most! I am assuming of course you mean “art” in the positive creative sense and not “art” as in “modern art”.

  • Rick O’Shay

    Since we’re covering stuff that is a large basis on which AR parts buyers base their purchasing decisions, can you guys also address barrel linings and finishes. Thanks.

    • Pete – TFB Writer

      Good idea. Will do.

  • One of the fathers of CHF barrel technology, Gerhard H. Appel attempted to bring CHF barrels to the American market in the 1950s. Alas, Appel was not equipped to deep drill or ream the barrel blanks prior to forging, and his source for the pre-drilled blanks had poor quality control. Others who remained in Europe, like Bruno Kralowetz of GFM GmbH, succeeded by providing the machinery to fabricate CHF barrels directly to manufacturers.

    http://www.gunsmagazine.com/1957issues/G1257.pdf#page=28

    The first US rifle company to offer barrels with CHF rifling was Weatherby circa 1959. However, their rifles were effectively sub-contracted out to European manufacturers, with only the final finishing and assembling done in the US. By the late 1960s, Remington and Winchester had procured their own hammer-forged rifling machines, and Ruger soon followed. By the early 1970s, Winchester was even forming the chamber and throat during the CHF process. This technology even filtered down to legacy models like the Model 94.

    • noob

      How do they get the mandrel out of the barrel after the barrel has been smooshed into it so hard that the rifleing has formed?

      • noob

        I finally found the answer – the mandrel is mirror smooth just like the inside of the barrel blank. Both are covered in lube and the lube is continuously added throughout the process. The mandrel can either remain stationary relative to the hammers and the blank fed past it, or it can move with the blank and then pulled out with a hydraulic press that also rotates it, like unscrewing a bolt from a nut.

  • DanGoodShot

    So.. using my 28oz eastwing won’t work!? Damn. I guess I have a new paper weight now.

  • Rnasser Rnasser

    By FAR, the leading manufacturer of hammer forging machines in the world is GFM GmbH of Steyr, Austria (the original place where the process originated). I would guess 90% of western made CHF barrels are made in equipment made by them.

    • No, the process is older than GFM GmbH, which was founded in 1945. It is my understanding that the basic CHF process originated at Gustav Appel Maschinenfabrik in Germany prior to the Second World War in order to form hypodermic needles. After the war began, the firm was chartered to apply the process to the manufacture of firearm barrels. Note that at least one of the founders of GFM GmbH, Bruno Kralowetz, had been previously employed by Gustav Appel Maschinenfabrik. Here are a few of the patents assigned to Gustav Appel Maschinenfabrik that list Kralowetz among the inventors.

      https://www.google.com/patents/DE768148C?cl=en
      https://www.google.com/patents/DE768149C?cl=en
      https://www.google.com/patents/DE1053287B?cl=en

      • Rnasser Rnasser

        You are right, but I was talking only about the geographical location (Steyr, Austria) where the process originated. Sorry for the confusion.

  • M

    Just an interesting pic. Before and after CHF

  • Emperius

    @disqus_ZuGaHtxUMf:disqus@disqus_0cUFy6XGuu:disqus@williamdeweese:disqus@disqus_LhVttSiPLj:disqus@disqus_QfLApSh0kU:disqus@mystick:disqus@lalahsghost:disqus@danielewatters:disqus@aussienoob:disqus@disqus_ROSkdtb1eO:disqus@rnasserrnasser:disqus@DanGoodShot:disqus@disqus_vD1G5zbTJS:disqus@disqus_5jxOuxOxDa:disqus@gusbutts:disqus
    Anybody know of a barrel manufacturer that produces cold hammer forged, nitrided barrels at 10.5″ or 11″? SAND Forging and APOC Armory are the only ones I know but none offer carbine lengths.

    • Rick O’Shay

      Check Daniel Defense. Last I checked they had some 10.3s for around $300.

      • Emperius

        Ah yes thanks. It is a .300 blackout barrel though. 5.56 is quite difficult to find.

        • Emperius

          @disqus_ROSkdtb1eO:disqus
          Oh? Is it nitrided for 5.56? I may have missed it.
          edit: comment disappeared, disqus having issues.

          • Rick O’Shay

            Yeah, they don’t like link posting. Probably think I’m trying to sell something. It’s a heavy phosphate finish and chrome lined barrel. Also out of stock… but they offer it.

    • Edeco

      Hmmm, not my department. Takes me a while if ever to get used to relatively inefficient use of consumeables (ammo in this case). Not that I’m against it, there are cases where, you know, carthago delenda est. But that’s where I’m at with AR’s.

    • Sasquatch

      Next time be a tad more specific.

    • Too busy for genuine looking, but Green Mountain – “GM-M26 10.5″ 5.56mm NATO 1:7
      $99.00”

      They have higher quality ones on other parts of their site. I just looked on “Military Barrels”

      • Emperius

        Nitrided is absent though, and not cold hammer forged. thanks.

  • Emperius

    Not cold hammer forged. thanks though, realized it is difficult to find such combo.