Specific hit locations are an optional rule in AToW, and separate from the conversion rules to TW from the Companion. Mixing specific hit locations and TW scale weaponry is a recipe for a migraine.
Seriously... if a Medium Laser hits the "left arm" of a single infantry trooper, what's it doing to the rest of the squad/platoon?
Showering them with vaporized blood and bits of flesh from the medium laser dumping so much energy into and through the person's arm to make it explode. Should I quote the
Only War critical hit section referring to energy damage to the arm to give a better idea?
In Only War, only the highest armor for a location is used (so if you have an armored chest plate providing 5 pts, a Jacket providing 3 pts to everything but the head, and a helmet providing 2 pts of armor, you get 3 pts protection to the arms and legs, 5 pts to the torso, and 2 pts of protection to the head. In Only War, armor and ROUNDDOWN(Toughness/10) is subtracted from the damage rolled. There is subdermal armor that adds 2 pts of armor to every location, but that requires lots of surgery and has its own penalties.
Daemion's idea about using the weakest armor rating for the trooper might make more sense since we are dealing with anti-vehicle weaponry being used against infantry (so that infantryman above would only have 2 pts of protection). For infantry vs infantry, using an average of the highest value of each location would work better.
So when designing an infantry unit, you record the highest armor rating on each of the locations, and averaging it by number of locations. So if your infantry unit protected its troopers with multiple layers on the torso (armor ratings 5, 8, 13, and 14), that means the troopers only have armor 14 at that location. If there are 5 other locations with no armor, that 14 is divided by 6, meaning the average protecting is 2.333 armor rating for vs infantry weaponry. For anti-vehicle weaponry (i.e. anything Mech-mounted), you would use the lowest armor value. So if the troopers still had their torsos protected by the 14-rated armor, had also purchased 12-pt armor on the arms and legs, yet nothing protecting their heads, the lowest armor rating is 0, and that is what determines their protection vs Mech weaponry.
Infantry should not have a lot of detail for Battletech tabletop combat. If your main concern is the 20-100 ton Mechs, then don't add extra details to the infantry unit that hve to be kept track of during combat. You set up the specifics when creating the infantry unit, then just put the basic information on their combat data line (5-6 of which fit on a single A4 sized sheet of paper).
Back to the idea of discount weapons/armor, how about if a unit using discount weaponry loses 1 pt of infantry protection each time it is attacked by a Mech or Mech-scale weaponry? So the infantry unit starts with 2 pts of armor. It gets hit by a medium laser, which kills off a trooper or two, but the rest of the unit has its armor marked down by 1 pt. A couple turns later the infantry platoon gets hit again, losing another couple troopers, but the infantry unit's armor is reduced to zero. Hopefully the owning player is pulling that infantry unit out of line of sight, otherwise the next hit is going to do a lot more damage. So Discount armor can provide a little bit of protection initially, but sustained hits mean the unit will soon be a liability in combat. But this is Battletech, where life is cheap.
