The Combat Shotgun is a high-powered shotgun which was made in MaD lab by XSpeedDemon.
When triggered, the Combat Shotgun will fire six, highly damaging andfast-moving bullets. The bullets slowly spread out. Upon touching a wall or floor, these bullets may disappear or bounce off and then keep bouncing until they eventually disappear. It is somewhat the same thing that happens when the bullets touch a doll.
If resized to size 600 before being fired, you can see that the projectiles launched by the shotgun are actually just really small and very fast moving dodecagons that do a lot of damage.
Pausing the game right after shooting the gun and then using the detail tool on the projectile will display the name of the projectile as "item".