In your mind, you have to be that 99.9% or even 100% sure that for that particular shot, you're going to kill. If your mind is saying 'well actually, I'm not quite sure, the wind is a bit gusty today, this may just wound' then you shouldn't be taking the shot.
That's my point.
Vent, the Exocet will do you just fine. But if you can borrow a rifle then that's an even cheaper option!
One other thing to consider. Are you the land owner?
If not, then by law you MUST get permission (ideally written) from the land owner before shooting pest species (this includes maggies). If you don't have the explicit permission from the land owner you could be guilty of armed trespass.
Then also remember that you are only legally allowed to shoot them if they are doing one of the following.
1) Threatening wild bird populations.
2) Endangering public health
3) Spreading disease
4) Causing serious damage to livestock, crops, fisheries, young trees or waterways.
Worth remembering.
K.