I’m glad you wrote, because using a heat gun on lead paint is dangerous. The lead compound in the coating vapourizes at temperatures higher than 700F, entering your body through your lungs. Don’t ever strip lead paint with any kind of torch or high-temperature device.
A safer thermal option for softening paint is heat delivered by infrared radiation. A new electric device called Silent Paint Remover raises the surface temperature of painted wood to 300F to 400F, softening old coatings and window putty in the process, but leaving lead in solid form.
Have you tried either one of two chemical products called Citristrip or Organistrip? Both are safe and work very well in my experience, even on old, multi-layer paint.
You’ll find a set of curved cabinet scrapers a big help cleaning the concave areas of your trim regardless of how you soften the paint. You’ll find them at specialty woodworking supply outlets.