You should perhaps describe what exactly you want this script to do. Your present description does not entirely make sense. If you are defining a rectangular area, is the angle you describe simple to rotate the rectangle? It seems to me what you want to do is:
Define a source volume and a target volume. A bullet is created at a random point inside the source volume, and sent flying at high velocity to a random position within target volume.
At the heart of the matter is how to calculate the direction vector from source to target. To do this you calculate the difference in position to make a vector, divide the vector by its length to give it a unit length, and then multiply by the desired bullet velocity. I have no idea what the bullet velocities in OFP are, but I'll make it 300m/s.
i.e.
_bulletvelocity = 300
_dx = (_pos_target select 0) - (_pos_source select 0)
_dy = (_pos_target select 1) - (_pos_source select 1)
_dz = (_pos_target select 2) - (_pos_source select 2)
_length = sqrt(_dx*_dx + _dy*_dy + _dz*_dz)
_velocity = [_dx/_length*_bulletvelocity, _dy/_length*_bulletvelocity, _dz/_length*_bulletvelocity]
Also, try searching the forums for
covering fire or
suppressive fire or
camcreate bulletThis should get you started