There was a thread in the Scripting Help section about something like this.
I linked to this thread:
http://forums.alliedmods.net/showthread.php?t=75882
You can use that to make random spawns.
Then you can create 1 ammo box each round start in a random spawn point.
If you don't know how to:
- create an entity
- hook when an entity is touched
- hook round start
- choose a random spawn from the list
Then you can search because all of that has been demonstrated plenty of times.
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