This concerns units which have turret machineguns, sometimes pointing away from the direction main gun is facing (those would include, for example, some Japanese tanks).
The idea is this: implement TargetWeight callin for the turreted MG weapon(s) that compares direction to the target unit to current turret rotation, and sets weight to 0 for targets outside machinegun’s fire arc. This way the MG fires at targets of opportunity correctly, but won’t cause the turret to rotate thus breaking aim for main gun.
This can only be properly implemented in LUS as COB has no (easy) access to info about relative piece rotations so can not know where the turret is facing now.
Advantage would be that turret MGs would function correctly - they do not currently (test with a tank vs inf and see that MG starts firing at things way before turret turns to face them).
Drawbacks are potentially heavier CPU load from having to compute angles to every suitable target in range every time the weapon retargets (no idea how much load that would actually cause)