As far as I know, UPS use seems to be counted separately to ammo, while a gun can only have one ammo type. It would probably be easier to make a small alcohol powered UPS recharger and let it power the gun.
Alternatively, you could make it so instead of reloading the gun normally you activate it to fill it with ammunition and alcohol, then convert it to a separate activated item with a certain number of charges, then convert it back to the empty version when it’s empty.
Only just realized this was necro, not sure why it showed up on my suggested topics?