For my take on the IK setting I created the following new weapon quality:
Ammo (#): The weapon is loaded with this many shots/uses. When empty, it gains the Load (1/3rd Ammo) quality. Example: The Cygnarian sentinel's Chaingun has Ammo (12). This means that after it has expended its 12 shots (of belted ammunition), it acquires the Load 4 quality to represent loading a fresh belt.
Two other weapons qualities that go along with the IK's firearm theme are:
Automatic: When firing this weapon the user gains the following trick:
Autofire (Ranged attack trick): You may target up to three targets, roll separate to hit rolls for each target. These do not have to be different targets. Each targetís to hit roll suffers -3 to hit and the weaponís Error range increases by +3 for the duration of this action.
Single Mode (named trick): When the named trick can be applied to an action with the weapon, it must be, before any other tricks are applied (if applicable).
The Chaingun has all three of these. The end result is that the Chaingun can only be fired in conjunction with the Autofire trick from the Automatic quality and can fire 4 three target bursts before needing a new belt fed into it. Only if the firer has the ability to ignore the Single Mode (Autofire) quality (through a class ability or feat, perhaps) would a single shot or other trick be applicable thanks to these qualities. Also, a class ability or feat that allows multiple tricks to be applied to the ranged attack (such as with the martial artist's Masterís Touch I ability) would let you do more with the weapon than just spray and pray.