They can be very tight which usually is a good thing so you don't end up like David.
If you dont have a pusher which most of us don't, you need a rock solid padded vise. If your using a brass punch and not getting anywhere, tape up all around the sight and one layer of tape on the edge of the sight and switch to a steel punch, that should give a solider hit and get it to move.
Penetrating oil or a little heat added, not a lot of heat, heat gun.
Don't give up, it's worth it in the end.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."