Hi, welcome to the forum.
There are lots of ways. Did you think of any ideas?
A couple of ways..
You can have a variable MouseEnabled which can be 1 for mouse enabled or 0 for mouse disabled. Set it to 0 when ammo=0 and 1 after reload. On your mouse events, also have the condition that this variable = 1
Have the mouse events in a group, and disable the group when ammo=0; enable it after reload.
Be sure to search forum and tutorials. For sure you will find something.