With ammo dice hits you have two choices, either:
* You increase the damage to a hit, or
* You can hit another target. This will cause weapon damage to another target. You can select the primary target again, he is technically both the primary target and also the secondary target of your burst. This requires that you have at least one bullet per target, even if you decides to hit the primary target with an ammo hit as well.
If you shoot one bullet with ROF 1 and you get a base hit and an ammo hit, you will hit the primary target and it will cause weapon damage +1.
If you shoot two bullets with ROF 1 and you get a base hit and an ammo hit, you can either hit the primary target with weapon damage +1
or hit the primary target twice, both hits will cause weapon damage
or hit the primary target and a secondary target and both will take weapon damage.
But I am not the writer of the game of course so
edit: also, I hope this was the question