I'd personally rather do something like this:
Gauss rifles and PPCs may use capacitor arrays to increase their battlefield performance.
PPC Capacitor
Each PPC capacitor must be connected to a specific PPC, increasing that PPCs weight by 1 ton and its size by 1 space. A critical hit to any part of this system disables the entire weapon. A PPC may only hold 1 capacitor per 5 full points of damage that the base weapon could inflict.
During the weapon attack phase, the attacker may choose to charge one capacitor attached to a PPC, instead of firing that PPC. Charging a capacitor generates 5 heat.
During each turn that a PPC does not fire, each charged capacitor attached to that PPC generates 5 heat. Additionally, if a PPC suffers a critical hit while one or more of its capacitors are charged, it discharges an amount of ammunition explosion damage equal to 5 x the number of capacitors charged on that weapon, and each of the weapon's critical hit slots suffers a critical hit.
When a PPC with one or more charged capacitors fires, its damage and heat are each increased by 5 per charged capacitor attached to that weapon. If the attacker's to-hit roll is a 2, the weapon overloads instead of firing, inflicting an amount of ammunition explosion damage equal to the maximum amount of damage the weapon would deal at its current charge to that section, and inflicting a critical hit on each of that weapon's slots. If two capacitors were charged, the weapon overloads on a roll of 2-3, and if three capacitors were charged, the weapon overloads on a roll of 2-4. Once the weapon has been fired, all of its capacitors are considered discharged.
Example:
Chen's Battlemaster has been modified, replacing the right arm weapon with a Heavy PPC with 3 capacitors, which weighs 13 tons and takes up 7 slots on that arm. On the first turn of the battle, Chen elects to charge one of the PPC's capacitors, rather than firing the PPC. This generates 5 heat.
On the second turn, Chen chooses to charge up the PPC's second capacitor. This generates a total of 10 heat - 5 for the capacitor that was charged last turn, and 5 more for the capacitor that was charged this turn.
On the third turn, Chen chooses to neither charge up nor fire his PPC. Since two of his capacitors are already charged, however, the weapon still generates 10 heat.
On the fourth turn, Chen chooses to charge up the PPC's third capacitor. This generates a total of 15 heat - 10 for the two capacitors that were charged last turn, and 5 more for the capacitor that was charged this turn.
Until Chen fires this PPC, the three charged capacitors will continue to generate 15 heat per turn.
Once Chen decides to fire the weapon, it will generate 30 heat and deal 30 damage, but if his to-hit roll is 4 or lower, the weapon will instead explode for 30 points of ammunition damage, delivered directly to the internal structure of his Battlemaster's right arm, and destroying the weapon completely.
Gauss Rifle Capacitor
Each Gauss Rifle capacitor must be connected to a specific Gauss Rifle, increasing that weapon's weight by 2 tons and its size by 1 space. A critical hit to any part of this system disables the entire weapon. A Gauss Rifle may only hold 1 capacitor per 7 full points of damage that the base weapon could inflict.
During the weapon attack phase, the attacker may choose to charge one capacitor attached to a Gauss Rifle, instead of firing that Gauss Rifle. Charging a capacitor generates 2 heat.
During each turn that a Gauss Rifle does not fire, each charged capacitor attached to that Gauss Rifle generates 2 heat. Additionally, if a Gauss Rifle suffers a critical hit while one or more of its capacitors are charged, increase the Gauss Rifle's ammunition explosion damage by 10 per charged capacitor, and each of the weapon's critical hit slots suffers a critical hit.
When a Gauss Rifle with one or more charged capacitors fires, its heat is increased by 2 per charged capacitor attached to that weapon, its short range is increased by +2 hexes per capacitor, its medium range by +4 hexes per capacitor, and its long range by +6 hexes per capacitor. The weapon's damage is increased by +2 per capacitor at short range, and +1 per capacitor at medium range.
If the attacker's to-hit roll is a 2, the weapon overloads instead of firing, inflicting an amount of ammunition explosion damage equal to the Gauss Rifle's base ammunition explosion damage plus 10 per charged capacitor, and inflicting a critical hit on each of that weapon's slots. If two capacitors were charged, the weapon overloads on a roll of 2-3, and if three capacitors were charged, the weapon overloads on a roll of 2-4. Once the weapon has been fired, all of its capacitors are considered discharged.
