Shotgun Pellets and Damage
Solution 1:
It seems like most shotguns, and the beam splitter mod, shoot 6 pellets. Based off several google searches on reddit and other stackexchange articles.
The damage per shot displayed is the total of all pellets, divide by 6 to get the damage per pellet. Damage reduction is applied to each pellet individually: so shotguns are very bad against high armor enemies. However certain damage adding legendaries (bleed, explosion) are also applied to each pellet, leading shotguns with these damage add effects to be extremely powerful against lower armor enemies, and even against higher armor enemies.