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Topic ClosedForged Steel Receivers vs Cast Steel Receivers

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Direct Link To This Post Topic: Forged Steel Receivers vs Cast Steel Receivers
    Posted: Mar 06 2017 at 8:38am
Forged Steel Receivers

First things First:
  1. Steel plants make "ingots" (large, and weigh tons) by pouring molten steel into a mold
  2. Ingots are hot rolled to make smaller "blooms"
  3. Blooms are further hot processed into smaller "billets"




  4. Billets are hot rolled into shapes such as flat stock, rounds and rectangular bar stock.




This is the most common terminology found in metallurgical textbooks.

USGI and Commercial Forged Steel Receivers:

In the true metallurgical sense, a billet is a semi-finished steel mill product. Gun receivers are not milled directly from a billet. The bar stock (rolled from a billet) is first hot forged to a basic shape then annealed (softened) to get a proper grain size to ensure a surface that can be properly and accurately machined.

  1. Start as bar stock from hot rolled billets
  2. Bar stock is cut to length (a little longer than the finished receiver length)
  3. Cut bar length is heated to 2000-2300ºF, then dropped forged to create a blank that is an approximate shape of the receiver.




  4. The blank is machined to the standardized dimensions of the receiver
  5. Machining is a multi-step process, it may be done at several different locations

    • All GI receivers were completely made by whoever the manufacturer was. This could be the prime contractor or their subcontractor. The receivers have markings identifying who made it and/or who they made it for.
    • Commercial Carbine manufacturers contract another company to make and partially machine the receiver, then finish machine the receiver themselves.

  6. Markings & serial number applied
  7. Receiver hardened
  8. Receiver parkerized, blued, etc.
Cast Steel Receivers
There are a variety of different types and means of casting. The one most common for firearms is Investment Casting, also referred to as Lost Wax Casting.

Investment Cast Steel Receivers

  1. Mold-maker creates an original pattern from wax, clay, wood, plastic, steel, or another material
  2. A mold, usually steel, known as the master die, is made to fit the original pattern
  3. Wax is poured into the mold to create a wax replica of the part that is to be made. The wax and replica it makes will be slightly larger to compensate for the shrinkage that the molten steel will encounter during cooling
  4. The whole wax assembly is dipped or sprayed with a ceramic slurry, and allowed to harden




  5. The whole wax assembly is then heated, so the wax will melt and run out of the slurry mold,
  6. Molten steel is poured or forced into the solid slurry mold by applying positive air pressure or other forces (injection, gravity, vacuum etc)




  7. Once the molten steel has cooled, and is solid, the parts are mechanically removed from the slurry shell




  8. The casting is machined to remove excess metal, mold lines, etc.

    • Commercial Carbine manufacturers contract another company to make the receiver, machining the receiver can be contracted out or done by the manufacturer themselves.

  9. Markings & serial number applied
  10. Receiver hardened
  11. Receiver parkerized, blued, etc.

The Real Questions

Each method has its Benefits & Disadvantages but both methods can produce quality receivers capable of handling the forces exerted on a firearm receiver. The metal alloy most commonly used in the manufacture of M1 carbine receivers, both forged and cast, is 4140 steel.

The Question of Quality and Strength isn't Forged vs Cast, it's:
  • Was the particular method done properly, as improper with either method is equally a fail

  • Was the receiver machined and machined properly, as no machining or improper machining with either method may affect safety and quality control and is a fail

  • Was the receiver hardened properly, as improper via either method is a fail. Receivers should be heat treated to 35-45 on the Rockwell C scale for proper hardness.



Arguments for and against Forged vs. Cast sometimes include a comparison of the grain flow of the metal. Solid steel bar stock (center) is drop forged before machining a receiver to form the grain pattern necessary for proper machining (right). Receivers cast properly will form a grain pattern different than that of the forged steel bar stock but equally as machinable as the forged steel solid bar stock.

--------------------------
Videos recommended for further visuals and learning:

Ruger, Part I
https://www.youtube.com/watch?v=ZBYw1CT2JiU
Ruger, Part II
https://www.youtube.com/watch?v=oriEUaJJEuU
Ruger, Part III
https://www.youtube.com/watch?v=PO4Lpr-mveA

Lamothermic (casts new carbine receivers for Auto-Ordnance & Inland Mfg)
https://www.youtube.com/watch?v=FS0uM3OC76I

Pennsylvania Precision (non-firearm excellent presentation on investment casting)
https://www.youtube.com/watch?v=wMzSS3BnMLs
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Credits:

This article was prepared with the assistance of Ted Syme. Ted is a retired metallurgist who is currently a licensed gunsmith who specializes in .30 caliber carbines.
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