What does the author warn against when it comes to DIY trigger jobs?

The warning about DIY trigger jobs emphasizing the potential for heat damaging the temper of trigger springs is significant. Trigger springs are precision components made from specific materials designed to operate under certain conditions. When modifications are attempted, especially those requiring heat, such as welding or grinding, there's a risk that the springs could lose their hardened characteristics. This change can affect their performance and, subsequently, the reliability and safety of the firearm.

Maintaining the integrity of these components is crucial. If the temper of a trigger spring is compromised, it might not provide the required tension, leading to malfunction or failure during use. This issue highlights the importance of understanding the materials and methods involved in firearm modifications and the potential risks of altering factory settings without appropriate knowledge and tools.