Tom,
What Rich said, as that's a very good description of the process.
I'll just add to clamp your trigger piece between two metal plates to keep the vise from maring it. And if you're making a trigger with a lot of curve to the shoe, you can cut a bit of a half moon in the plate to help create the curve.
Then just tap tap tap,,,, well maybe a couple hundred times or so! No heat needed.
John