"A compact, wide-caliber slug-thrower. Very short range, but it packs a punch and handles quite well."
The heavy SMG is a moderately-heavy, multi-shot firearm in RimWorld which fires a burst of 3 slightly-lower damage shots; has a moderate time between shots in a burst; a moderate time between bursts; short range; and moderate accuracy.
Although the heavy SMG is limited strictly to close quarters combat, it is a surprisingly powerful close-quarters weapon, owing to its burst-fire nature and its decent stopping power for a burst-fire weapon - resulting in a weapon that can take somebody down quickly in the hands of somebody that's trigger-happy. Very effective against poorly-protected flesh; a few lucky (or unlucky) heavy SMG shots may remove a limb, and will instantly destroy any digits or toes. In regards to brain shots, the heavy SMG is a strong contender too; even a well-protected noggin won't be sufficient to stop one of the heavy SMG's 'wide-caliber' bullets from sailing through the metal plating of that sturdy advanced helmet, and rendering the wearer unconscious - or debilitated.
As the heavy SMG won't see any use out of close-quarters combat, it's a somewhat skill-friendly weapon that should still be considerably effective in the hands of a shooter with 95% accuracy per tile; this is achievable with a level 5 careful shooter; level 6 standard shooter; or level 8 trigger-happy.
Heavy SMGs can be purchased from outlander combat suppliers and towns, or from orbital weapon traders - or from incapacitated outlanders, pirates, and mercenaries. Heavy SMGs can also be crafted at a machining table once the machining research is completed; from 75 steel, 4 components, and 28,000 (466.67 secs) of work.
Conclusion & Comparison
The heavy SMG is a solid weapon where it counts, and is actually one of the best in its class; it has a significantly higher damage output than the slightly more-expensive LMG, and cheaper pump shotgun - and even has a longer range than the latter - although the DPS gap over both weapons narrows considerably towards the upper-extremes of the heavy SMG's range as accuracy steps in as a bottleneck. In terms of stopping power, it actually does more damage per shot than the mighty (and much, much more pricey) charge rifle, and even has better damage output at 5 and less tiles - although the charge rifle still dominates the heavy SMG in accuracy (from 8 tiles onwards), range, and time between bursts, and is still the better weapon overall.
Although the mere 18 tile range may seem like the heavy SMG's number one limiting factor, its accuracy severely hinders its damage output beyond 18 tiles - with its DPS being only similar to the assault rifle's by 20 tiles.
The heavy SMG is most useful mid-game, but is still a competitive weapon late-game as it benefits significantly from being of higher build quality.
The Heavy SMG seems to take it's appearance after that of the TEC-DC9 Semi-Automatic Pistol in real life, albeit Full Auto in RimWorld. The Intratec TEC-9, TEC-DC9, or AB-10 is a blowback-operated semi-automatic pistol, chambered in 9×19mm Parabellum. It was designed by Intratec, an American offshoot of Interdynamic AB. The TEC-9 was made of inexpensive molded polymers and a mixture of stamped and milled steel parts. The simple design of the gun made it easy to repair and modify.
The below graphs assume an unmodified shooter using a Normal quality weapon.