I did it once and it was a BEAR! Heat and chill multiple times, then heat and cool with penetrating oil. 40 oz hammer and a hardened 3/16 punch etc.. Still no movement? Use your large vise to press against the smaller side of the pin as you would press out a U Joint from a yoke. The pins and sight frame metals may have bonded slightly. Unless it's a gourmet barrel (Hart or Krieger). If so, I'd defer the job to a gunsmith. I simply don't have the personal fortitude to pummel pieces of art.