As an alternative to torch heating the firing pin, try freeze-thawing the bolt a few times. The concept is the same, but without the risk of destroying of the heat treatment. Once the bolt is back at room temperature, try to remove the pin.
Spraying the thread area with upside down "dust remover" spray is effective. Wear gloves and goggles. A minimum of exposed skin is the goal -long sleeves etc. Do not aspirate the fumes. Do this in a well ventilated area. Also, don't drop the bolt when it is frozen. depending what you are using to cool the bolt, and the steel, it may be very brittle. There are reports of steel from some of the WWII liberty ships becoming brittle at temperatures close to the freezing point of water.
If you give the bolt a generous coat of penetrating oil beforehand, some might wick into the threads as it thaws. This will also help protect against condensation.
If freeze/thawing does not work after a few tries, then try torch heating. The combination of techniques may do what either does not.
I learned this trick from an auto mechanic friend of mine who uses it to remove seized bolts from gas tanks. for obvious reasons the application of heat to these areas is problematic.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.