It sounds like you have a Classic front sight. If that is the case, you don't drive out the pin. You just clip in the new sight. Look at the front of the sight base and see if there is about an 1/8" hole. If so, it's the Classic clip on style. There is a spring loaded pin in the rear portion that helps retain the sight.
If you want better retention you can drift out the pin, get the spring and plunger out, stretch the spring a bit, or get a stronger spring and reinstall the parts. The punch for the pin should be about .050.
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