Hmm
, to me the most likely culprit is AI, I havnt been editing for awhile now and dont know if anything has changed in ARMA but if you have the sniper in a group and the group leader defaults the unit to "safe" or "hold fire" you're in uncertain territory, the unit may or may not fire.
Try removing the sniper from any groups, setting his behaviour to "combat" or above (see comref under 'setbehaviour' for more details on how to do this) and try Garcia's code again. This way nobody will be telling your sniper not to fire!
As far as I am aware there are some really nice bullet camera scripts out there too, could be a nice addition to your cutscene
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If this fails it would help if you could give a fuller description of your script and what actually happens in this section of the cutscene, maybe a copy of the mission??