This sounds really cool, I definitely like the overheating idea. You might try making it a little more flexible though. Like a cross between 40K plasma weapons and the ones the Covenant use in Halo.
Have three different firing modes with variable rates of heat generation all going to a single pool of 100 “ammo” representing the heat capacity of the weapon.
- Semi-Auto: Heat generation of 5 per shot. (20 shots total before overheat). Cannot fire if heat level is at 100. 30 UPS per shot. Same damage & range as present.
- Burst Fire: A five round burst at the same energy consumption and heat per shot as single fire.
- Overcharge Shot: Fires a single powerful shot, (might consider having a small explosion with a 3-5 tile diameter). Requires 50 heat and 300 UPS. You CAN fire it in this mode with heat greater than 50, but if you do it will have a catastrophic overheat, hurting you and damaging the weapon.
Balance Considerations: Cannot accept grenade launchers, shotguns, or flamethrowers on the underbarrel slot, as the heat generation from firing would risk cooking off the ammunition.
Alternative Suggestion: I recall in Mass Effect 2 the weapons used disposable heat sinks as magazines. This might have merit as a reloading mechanic here as well. I would suggest making them reusable though, but rare to find and difficult to manufacture yourself, requiring superalloy plates or something.