maybe you don't need it to draw power directly from the armor, but have the ammo "rechargeable" by putting it in a machine, and after a bunch of power goes into it, it outputs full ammo, idk if this works exactly, since nothing is left over after ammo is used up but it would be cool to have laser weaponry work this way.
Thank you for the idea, we are currently working on the BFG (its nuts!). the mod is intended to add overpowered "laser style weapons" for fun and to be a small learning experience for us. we'll consider the idea, maybe it could be the next ammo type!
I like the idea of recharging your ammo in a machine. Perhaps have it so that there is a separate item called "Depleted Laser Ammunition" which is automatically created after a round of Laser Ammunition is used up, which can then be put into a machine to be recharged into Laser Ammunition. Another option is to have an item that you can install into a module suit which will automatically "craft" "Depleted Laser Ammunition" into Laser Ammunition while draining your suits energy.