In the mission editor
1. Place any vehicle, with player as gunner. Setting the ammo slider all the way to the left (no ammo).
2. (optional) Save mission. Open mission.sqm in text editor and verify "ammo=0"
3. Start mission. Note you have full ammo supply.
4. Return to mission editor. Increase ammo by one click of right arrow.
5. (optional) Save mission. Open mission.sqm in text editor and verify "ammo=0.0099999998;"
6. Start mission. Note you have very little ammo.