Mike George
Nitro-cellulose cartridge propellants need to generate high pressure very quickly in order to burn at the right speed, and the eight-star crimp needed more pressure to open it than the conventional six-star – or so one leader in the shotgun cartridges business told me.

However, there were manufacturing problems with the eight-star.

Some cartridge cases needed to have their wall thickness tapered towards the mouth in order to seal properly, and it is much cheaper to standardise as much as possible when designing a range of cartridges.

Personally, I have never noticed any marked difference in performance between six-star and eight-star shotgun cartridges.