M1 Carbine Reduced Aperture Kit


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This is a kit to reduce the size of the late model apertures on the M1 Carbine. This is a legal modification for the CMP ‘as issued’ class.  This modification has not been evaluated on the earlier style flip-apertures.  It might work, but has not been tried.

You do not need to remove the aperture or sight from the rifle to reduce the aperture.

The kit includes a #45 drill bit, a #3-56 plug tap, a 0.050″ Allen wrench, a threaded set screw with a 0.042″ diameter hole, and Loctite.

Tools you will need:

  1. a tap wrench that is adaptable down to a #3-56 tap.

Steps for reducing the size of your M1 Carbine aperture:

  1. Use the #45 drill bit in the aperture hole to smooth out the hole to a consistent diameter.  This should remove very little material as the USGI aperture is almost the exact size for the tap.
  2. Use the #3-56 plug tap (with your tap wrench) to tap screw threads into the aperture hole.  Apply a few drops of oil to the tap before starting.
  3. Place a small drop of Loctite on the outside of the threaded set screw.
  4. Insert the threaded set screw, using the allen wrench, into the threaded hole in your aperture.


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