Also, I may be wrong but of all the second hand stories I've heard about it there never seemed to be a serious injury to the shooter which seems surprising?
Or have I just missed the 'tales of lost fingers'?

The chain fire occurring from behind the nipples would seem to make a good case for the replacement nipples to use Shotgun primers wouldn't it? It seems that they would contain things a bit better? (Taking their extra pressure into account when deciding on charge I guess)