First, dont get horrified by the number of arguments, you only need to play with the array where you see the sin and the cos, this is the "sky" position where the bullets will go [x,y,z] when the target is objNull. In the example, 800m ahead of the shilka, 100m alt.
You may also play with the "smoke type" argument (---> 0, 0.5, true, false, false)
0 means no smoke, 1 to 5 are different types of smokes for the rounds, for example 5 for a thin smoke trail (---> 5, 0.5, true, false, false).
The first array [0,2,2.5] indicates relative position from the center of the firing unit [angle, radius, altitude], in this example, 2m ahead, 2.5m high (where the guns of the shilka are placed).
Lets say your shilka's name is shilka
Each call to this script will fire a "Bullet4x23" round from the indicated unit (shilka) to the indicated space position.
Just execute it with the desired frequency at the desired positions.
[shilka, objNull, 300, 0, 0, 0, "Bullet4x23", "", 1, 0, [0,2,2.5], [(getPos shilka select 0)+sin(getDir shilka)*800,(getPos shilka select 0)+cos(getDir shilka)*800,100], 1, 0, 0.01, 4, 2, 0, 0.5, true, false, false]exec"mandomisil.sqs"
Find the script attached to this post, just copy it into your mission folder.
It is part of the mandomisil suite currently available at the Resource Betatesting forum.