How to Mill a Lower Receiver

A weapon's receiver is the part of the weapon that houses the operating parts. Parts include the trigger mechanism, magazine well and bolt carrier group. Most firearms have a solid, single receiver. A lower receiver is only implemented on select weapons, particularly with assault rifles such as with AR-style firearms. The receiver is typically machined from steel or aluminum stock using a mill. Specific cuts are made in order to fit other parts to the weapon. Milling a lower receiver will vary according to your blueprints, but involves universal steps.

Things You'll Need

  • Steel or aluminum block
  • Mill
  • Receiver blueprints
  • Metal brush
  • Mill bastard file
  • Rotary tool
  • Buffing and sanding attachments
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Instructions

    • 1

      Mark out the cut design on the lower receiver block, both depth and length, using a stencil or design template. As all lower receivers vary in construction, your design will vary. Pay specific attention to your blueprints when stenciling the cuts.

    • 2

      Set the mill to the specific depth and angle points. If working with a CAD system and nose end-mill, plot the coordinates and angles into the computer. If using a traditional end-mill, set the dials to the proper depths and angles for your cuts.

    • 3

      Secure the work-piece to the mill appropriately. Start the mill and feed the block into the mill. Lower the mill onto the stenciled lines until the bit begins chewing through the metal.

    • 4

      Stop the mill frequently to check your work dimensions. Once the milling is complete, a bit of touch-up work will be needed. Brush away burring and nicks using a steel brush and metal file.

    • 5

      Measure all cuts and angles using a dial caliper and a micrometer according to your blueprints. Correct any edges that are off using a mill bastard file. Brush away any metal shavings. Polish and buff the metal to a smooth finish using a rotary tool with a buffing attachment.