Look at buying a MAPP torch. I bought mine at Home Depot. They’re cheap and pretty safe. They deliver a lot more heat quickly than a heat gun. It’s no acetylene torch, so you don’t have to worry about melting metal. The faster you heat the magazine tube, the less heat will wick into the receiver. It has an igniter in the trigger so it’s easy to ignite and shut off. No mixture knobs to mess with or anything. If you can operate a BBQ igniter, you can operate this torch. Apply the heat to the base of the steel magazine tube and rotate it around the tube evenly. Apply heat for 20 seconds, try to unscrew the tube. Apply more as needed.
https://www.homedepot.com/p/Bernzomatic-BZ8250HTKC-MAP-Pro-Hose-Torch-Kit-BZ8250KC/203391035
Same one I have. After 6 years or so, I’m still using the same bottle.
Getting a vise is a good idea. Get some padded jaws to avoid marring your work. Check where you’re clamping carefully. You don’t want things like the trigger pin under the clamping area.