It does not shoot at all. This question is, of course, only relevant if there is a chance for the firing model to be hurt by its own weapon.

Though most often a battle will be decided with bloody close quarters fighting, hails of crossbow bolts and deadly cannonballs can soften up the enemy for the final charge, or perhaps even panic them from the field without a fight. Once the movement and magic phases are over, it is time to work out shooting. Troops armed with bows, crossbows or other missile weapons may shoot at any enemy targets they can see. Unless otherwise specified, each model can only make one shooting attack in each shooting phase. You may also shoot with any war machines such as stone throwers, cannons, etc. You always start shooting with any weapons that require you to guess the range of the shot (such as cannons and stone throwers for example). Guess all the ranges of these before measuring any of them. Next, resolve the results of these shots using the rules described in the War Machines section. Once this first part is complete, continue on to the rest of your shooting. Nominate one of your units that you want to shoot and select one enemy unit you wish your unit to shoot at. Once you have declared your target, measure the range and resolve shooting using the rules described. Then proceed to the next unit that is shooting and continue as above until you have shot with everything able to do so, including any non-guess range war machines you may have.

Shooting

Yes, this is possible in theory, but certainly not easy to achieve!

Warhammer Fantasy: 7th Edition

Shooting - Frequently Asked Questions
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If a model does not have line of sight to a target the rest of the unit is shooting at, must the model shoot (missing automatically), or does it not shoot at all?
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Can models get a better save than 0+ (i.e. a negative armour save)?
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Shooting - Frequently Asked QuestionsURL Copied!

If a model does not have line of sight to a target the rest of the unit is shooting at, must the model shoot (missing automatically), or does it not shoot at all?URL Copied!

Can models get a better save than 0+ (i.e. a negative armour save)?URL Copied!

Shooting - Frequently Asked Questions
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If a model does not have line of sight to a target the rest of the unit is shooting at, must the model shoot (missing automatically), or does it not shoot at all?
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Can models get a better save than 0+ (i.e. a negative armour save)?
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