Well that was easy. I knocked the sight out quick and examined it. It appeared that the original sight post went all the way down to the dovetail on the sight. I put it in the bench vise and stuck a punch down through the hole in the top of the sight hood and smacked it but it wouldn't budge so I drilled up through the bottom of it and it came right out.
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Next I went in my tool drawer and found an allen wrench that was just larger than the hole. Driving a hex into a round hole makes a nice secure interference fit that can still be easily drifted in and out.
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My first thought was spin it in a drill against the bench grinder to taper it down and make a fine target post.
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I tried that on the gun but my poor eyes just couldn't see it so I cut a new piece and left it full width and drove it in place with a brass hammer
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voila
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This just about fill out the rear sight notch so the size is about right for me. I'll adjust up/down left/right as needed