The pump shotgun is a moderately-heavy, single-shot weapon with slightly higher damage per shot, a slightly shorter time between shots, high accuracy, and short range.
Due to these attributes, the pump shotgun makes a great early-mid game close combat weapon due to its impressive damage output, but the handicapped range will be a limiting factor as more powerful, better-equipped enemies take to raiding your settlement. As typical with a short-ranged, faster-firing weapon, the pump shotgun's effectiveness won't be too badly hindered if it were to be equipped by a less accurate (<95% post-processed accuracy) shooter - and it benefits more from a trigger-happy than a careful shooter as a result. Its high stopping power also means that it's effective at crippling, or even outright destroying limbs and organs.
As tribal raiders don't get any better-equipped than plain tribalwear, and possibly a parka (which still offers little protection), the pump shotgun is a great counter against them as there will be little-to-no resistance from its impressive raw damage output.
Pump shotguns can be purchased from outlander combat suppliers and towns, and orbital weapon traders for a moderate price - or obtained via incapacitating a pump shotgun-wielding outlanders, pirates, and mercenaries. Pump shotguns can also be manufactured at a machining table once the machining research has been completed for 60 steel, 3 components, and 30,000 (500 secs) of work.
Conclusion & Comparison
Overall, when put up against other weapons in RimWorld, the pump shotgun really is just middle-of-the-road in its class: it's considerably better than the cheaper machine pistol in terms of damage output and accuracy, but still has a significantly shorter range which'll put the machine pistol at an advantage. However, the more expensive heavy SMG has a significantly higher (~32%) higher average useful DPS than the pump shotgun, as well as a slightly longer range - and the LMG has a significantly longer range than the pump shotgun, although the pump shotgun's useful DPS is actually slightly higher (~14.8%) than that of the LMG's.
Against its brand new burst-firing cousin, that is the chain shotgun, things get more interesting: while the pump shotgun has superior range to the chain shotgun, the chain shotgun still has higher overall accuracy than the pump-action shotgun - 3 times 41.1% (~123.3%) versus 82.5% at 8 tiles, the most likely range that both of these weapons would see a lot of use at - and the chain shotgun also has a higher damage output, and there's even more to come as the chain shotgun has a lot of unrealised potential in normal combat scenarios - but there's more information on that matter on the chain shotgun's page. However, the chain shotgun is considerably more expensive and also rarer than the pump shotgun.
- The pump shotgun seems to have the appearance of a variant of the Remington 870.
- In-game visuals depict it as firing a blast of pellets rather than a singular slug; however, it deals damage as if the target is hit by 1 shot.