Re: minimum weight
I have, enough to know I'd never want to do it unless there's no other choice.
I was reading an article a while back about that way of thinking; apparently, there is a real problem with civilians flying ex-military aircraft in that they really don't want to eject.
A substantial proportion of pilots who eject spend the rest of their careers flying desks thanks to spinal damage.
I think that might have been true for very early seats, but that was a long time ago. There's been lots of development on ejection seats.
The fact that this is related to the mass of the helmet indicates that this is related to the compression forces generated on cervical vertebrae when the eject rocket fires.
It;s the pilot's mass that is important. To my mind, that implies it's the deceleration on deployment that causes the problem.
Ejector seats clamp the pilot's head to the seat back during eject specifically to ensure that forces are vertical and to prevent whiplash injuries when the chutes open.
Errr - you sure about that? Because none of the seats I've played with do that...