On Eley Hawk webbsite is following:

Bismuth is a metal (Bi) alloyed with tin (Sn) to give similar characteristics to lead shot. Bismuth shot is manufactured in-house by Eley Hawk using the Bleimeister or “short drop” process, the same method Eley Hawk use to produce lead shot. The resultant shot
has similar properties to lead shot in a modern trap cartridge.

Niklas