I put one bullet enemy for each enemy, create instance id in both.
for each bullet order by iid ===> bullet.id=bullet.iid
for each enemy order by iid ===> enemy.id=enemy.iid
when bullet.id = enemy.id ===> shoot
wen the bullet is out of te label or out your owner limits, you can stop it, and put in pos(-1000,-1000) for example.
if need to have the same nbr of enemies and the bullets.
I made a game in this way a work perfectly.