Combat shotguns with the two-shot legendary modified causes it to fire 8+1=9 projectiles, instead of two shotgun shells, which would equal 16 projectiles.
Applying the advanced receiver adds an extra projectile per shot.
When equipped with a drum magazine, full stock, front sight ring, long barrel, and compensator, this weapon closely resembles the combat shotgun seen in Fallout 3. The only major difference is the placement of the magazine, which in Fallout 3 was placed in front of the ejection port.
Because the bleed damage is applied per projectile, a combat shotgun with the "Wounding" prefix inflicts massive damage per shot. The bleed damage will continue to stack with successive shots. With an advanced receiver, the weapon will deal 200 additional damage per shot over 5 seconds, if all projectiles hit the target.
The automatic receiver fires just one round in V.A.T.S., with no increase in damage compared to the single-shot receiver, while also adding a 25% increased cost to action point usage.
The combat shotgun and combat rifle share nearly identical models, with only a few differences.
When equipped with a bayonet and short barrel, the bayonet's model will clip through the shotgun's handguard.
Bugs
PC The damage of the explosive legendary variant of the combat shotgun is labeled wrong, while V.A.T.S. adds 15 damage to the total damage, the added damage is actually increased per pellet (7 pellets*15=105 Base, 120 W/ advanced receiver. Ranking up the Demolition Expert perk increases the explosive damage independently from direct hit damage). [verified]
PC The glow front sight ring does not appear in the Sights tab unless a front sight ring is placed in the player's inventory or a workbench, although it has no requirements and cannot be installed. This is because it is incomplete due to an oversight. It has no associated Construction Object, which determines the requirements to craft it, and shares a world object model with the front sight ring. The front sight ring's world object is called glow front sight ring, but it will only allow the installation of the front sight ring.[verified]
Gallery
A long barrel combat shotgun with a full stock, medium magazine and suppressor
Combat shotgun modified with a ported long and shielded barrel, marksman's stock, front sight ring, drum magazine and compensator