Metallic Sight Sizes

I feel like my metallic sights are a bit too tight in appearance, aka the gaps left and right of the front sight in the rear sight seem too small to me.  I measured them to be:

Range officer: Rear Sight Opening and Front sight Width 0.120in
Kimber Gold Match II: Rear Sight Gap 0.133in, Front Sight Width 0.137in

The Kimber seems to have a bigger gap to me, but both are a bit tight.  The RO is being turned into a Wad gun, so I'm not too concerned about that one.

How would I go about making the rear sight bigger on the Kimber?

Thanks!

Set up slide in mill and use a 1/16 cutter to open the rear notch up to desired width.

You can also use a thin pillar file to open up the notch, and then cold blue. Just make sure the file is less than 0.133" in thickness

Thanks KC!  You might have a little more work to do on my pistols.

I unfortunately don't own a file thin enough.

Is there no way to replace the aperture?

Sometimes its easier to just a a thinner front sight.

If you are a stickler for appearance, have a good machinist do the work. I've used a small safe-edge file to open the rear sight. File at a slight angle so the width at the back is slightly narrower than at the front of the blade. When it looked right, I used cold blue on the exposed metal. 

Depending on your personality the imperfections can be good or bad. If I can see the slight angle on the left side and the bottom corner that isn't perfectly square, then I know that I am focusing on the sight.