Give loon2 (the victim) an eventhandler:
loon2 addEventHandler ["killed",{loon1 setCombatMode "BLUE"}]
When loon2 dies loon1 will cease firing. This way you should be able to ensure that loon1 only fires as many bullets as he needs to kill loon2 (if he needs one, he will fire one shot only).
If the eventhandler reacts to slow (sometimes dead units are not registered at once) exchange the eventhandler to
loon1 addEventHandler ["hit",{loon2 setCombatMode "BLUE"}]
Or you could give loon2 an eventhandler "hit" and set him to setDamage 1 when it executes or...
Actually the possibilities are endless. That way you donÂ't need to mix with the contents of the loonÂ's magazines.