And finally, each gun has two attachment slots.
The type of frame you built your gun on will determine how many circuits are available (up to eight max). Then you can add circuits to increase or decrease a weapon’s stats (damage, reload speed, clip size, firing rate).
Likewise, you can turn a Military Engine into one of several assault rifle, sniper, or shotgun variations. For instance, a Pneumatic Torch engine will become a flamethrower with a Default Tip, and a Cryogenic Torch with a Precision Tip. Weapons can have up to two engines attached (so two guns in one), and then the type of tip you combine with that tool will determine its effect.