The problem is the "wait 2 seconds."
Everything after that action waits 2 seconds before executing, including the "Set Ammo to 10"
The rest of the game continues while those actions following the "wait" are waiting to execute. So since the Ammo is still 0, and the animation is still 9mm, that event is triggered every tick for two seconds, until the ammo is set to 10, which prevents the event from executing anymore. However there is a whole set of waits built up, so all those actions after the wait continue every tick for 2 seconds more, as all those waits run out.
I moved the "Set Ammo to 10" above the wait, and it seemed to work.