It's alright now. I looked for advice and was told than my home-made drift punch was too long and sprang back under the hammer. The pin was then started with a center punch and further taken out with a short drift. There was some rust on the pin which must have concurred in making it stick. Anyway, I polished and cold- blued the pin and used the very same to lock the replacement higher sight blade. All's well that ends well, my rifle's POI sits now just above POA at 100 meters. Thanks for the help.