The image in this answer shows Reed's body stretching under a massive impact.
I'm wondering what sort of impact would be too much for him to sustain, that would overload his stretching powers.
A gun shot generates a huge amount of force over a tiny area, so I'm thinking that would be a good candidate.
Has Reed ever ever been shot with a gun at point blank range?
The max Reed Richards can stretch his body to before it becomes too painful is about 1,500ft. A bullet from a 9mm can make it as far as 7217ft.
If someone could find an actual head shot, that would be awesome