"A magazine-fed fully automatic shotgun. Short range and very low accuracy, but extraordinarily dangerous."
The chain shotgun is a considerably heavy, 'automatic' firearm in RimWorld which fires 3-shot bursts of high damage rounds, very short range, and very poor accuracy.
Despite these caveats, the chain shotgun is capable of dealing out tremendous amounts of damage when spraying at clustered enemies, or at a single large foe due to the accuracy bonus received from doing so. Due to the fact that it's very short-ranged, the chain shotgun is a great weapon to equip even on people with very poor (<93% post-processed) shooting accuracy - without being penalised too badly.
One scenario where the chain shotgun could prove to be extremely potent is when used in killboxes, where the short distance and bunched up enemies allow this weapon to be unleashed at its full potential - but the improved AI in Alpha 17 could make this tactic somewhat less useful, and not everybody likes building killboxes as they take a lot of challenge out of the game.
As with most other ranged weapons, the chain shotgun can be purchased from outlander weapon caravans, and from orbital weapon traders - or obtained via incapacitating a chain shotgun-wielding outlander or pirate. Chain shotguns can also be manufactured at a machining table once the machining research has been completed; for 70 steel, 5 components, and 45,000 ticks (750 secs) of work.
Conclusion & Comparison
The chain shotgun has extremely high damage potential owing to its zero-compromise damage per shot, and triple-burst nature; it is literally the 3-shot burst version of the pump shotgun, and the LMG of the shotgun world - but its major caveats are its extremely handicapped range and accuracy, for the sake of balance to prevent this weapon from being absolutely insane. Against normal-sized targets, the chain shotgun still has superior damage output to the pump shotgun, but falls behind more accurate weapons such as the heavy SMG.
However, against larger targets where the accuracy gets a positive multiplier, and at higher weapon quality levels, the chain shotgun can even usurp the almighty charge rifle in terms of having the highest damage output out of any standard ranged weapon in the game - an impressive feat to be sure. As previously mentioned, the chain shotgun can also be used for point-blank crowd control, to make use of the many missed shots that will inevitably occur.