Castings vs. Forgings

date: June 26, 2018

Why does Anderson Manufacturing use forgings instead of castings for our uppers and lowers? Let’s start with a short explanation of the difference between casting and forging.

Anderson lower receivers after anodizing.
Anderson “Don’t Tread On Me” Lower Receiver.

Casting

Casting is the process of heating aluminum or other metal until it is melted and pouring the liquid aluminum into a mold that creates a desired shape. There are three main types of casting: Die Casting, Permanent Mold Casting, and Sand Casting.

Die casting involves forcing the molten aluminum into a die or mold under pressure. Permanent mold casting uses molds with cores of steel or other metal. In sand casting a pattern is pressed into sand to create a mold that is then filled with melted aluminum.

Some of the advantages of casting include:

  • There is no upper limit to the weight of a part you can cast
  • Casting allows the use of a big range of alloys
  • Tooling can be less expensive
  • Small production runs are easy to do

Forging

Forging is the process of applying heat and force to solid billets of aluminum or other metal to put the metal into the desired shape without melting it. The metal is heated in a furnace or fire and

then forged into shape using a hammer or a die. There are several types of forging processes: Impression Die Forging, Cold Forging Open Die Forging, and Rolled Ring Forging.

Impression die forging presses the aluminum between two dies. The dies create the desired shape of the part. This is also called closed die forging and is usually done with hydraulic or mechanical presses, and hammers. These presses and hammers can create up to 50,000 pounds of force.

Some advantages of forging include:

  • Forgings handle impact better than castings
  • Forging eliminates porosity, cavities, and shrinkage
  • A tight grain makes forgings mechanically strong
Left is a lower receiver after forging. Right is a lower receiver forging before forging.
Left is a lower receiver after forging. Right is a lower receiver forging before forging.
Top is a lower forging after machining. Bottom is a lower forging before machining.
Lower receiver forging after machining.

Which is Better For Rifle Parts?

According to a research paper done by the University of Toledo forging is better:

  • Forged parts had a 26% higher tensile strength than the cast parts. This means you can have stronger shackles at a lower part weight.
  • Forged parts have a 37% higher fatigue strength resulting in a factor of six longer fatigue life. This means that a forged shackle is going to last longer.
  • Cast iron only has 66% of the yield strength of forged steel. Yield strength is an indicator of what load a shackle will hold before starting to deform.
  • The forged parts had a 58% reduction in area when pulled to failure. The cast parts only had a 6% reduction in area. That means there would be much greater deformation before failure in a forged part.

This wasn’t a study of gun parts, but the results speak for themselves.