What does killshooter generally do?
"Killshooter" determines whether or not you can do damage to a friendly (same country).
With Killshooter "on", as it is hard-coded into the Main Arenas, shooting a friendly does not damage the other plane and instead inflicts the damage to your own plane/vehicle -- hence, it kills the shooter.
With Killshooter "off", if you shoot a friendly they actually take the damage (so you can have friendly-fire incidents). This is usually the setting in certain historical and squad events (like FSO).
It can be turned on/off by you only in custom arenas or offline.
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Ryno