S1897 is a pump shotgun that use 12 gauge ammo types and reload after 1 shots. S1897 can be random sometimes because the bullet pallet spread is bigger then any other shotgun. With the help of choke can make S1897 more predictable.
S686 is the two barrel shotgun which dose insanely high damage in close range. This shotgun fire 2 shots then reload but if you hit those 2 shots it will be most likely a win to you. Keep in mind if you play third person this shotgun is the way to go for you.