For a shotgun, you would need to use a custom firing script to shoot multiple bullets with a slight spread.
Try
function yourgunimage::onfire(%this,%obj,%slot)
{
%dir=%obj.getmuzzlevector(%slot);
%pos=%obj.getmuzzlepoint(%slot);
%spread=0.1;
for(%i=0;%i<5;%i++)
{
%p=new projectile()
{
initialvelocity=vectorscale(vectoradd(%dir,vectorscale(getrandom(-100,100) SPC getrandom(-100,100) SPC getrandom(-100,100),0.01*%spread)),%this.projectile.muzzlevelocity);
datablock=%this.projectile;
initialposition=%pos;
sourceobject=%obj;
sourceslot=%slot;
client=%obj.client;
};
missioncleanup.add(%p);
}
}