Ah, I think it might not be very well explained:
For example (making up numbers). If you have armour like:
AR:20
H: 2000
LA: 2000
T: 4000
RA: 2000
LL: 3000
RL:3000
Then you have your human body underneath it:
AR:1
H:10
LA:10
T:40
RA:10
LL: 15
RL:15
I shoot at you with an assault rifle with a BF of 25, damage 30 and shoot 100 rounds. If I hit your torso, I do 3000 (30 x 100) points of damage to the armour. Your armour will then be:
AR:20
H: 2000
LA: 2000
T: 1000 (4000-3000)
RA: 2000
LL: 3000
RL:3000
If, instead, I shoot at you with a low power rifle, BF of 15 damage 30 and shoot 100 rounds. If I hit your torso, I do 300 (30 x 100 and then knock off a zero). Your armour will then be:
AR:20
H: 2000
LA: 2000
T: 3700 (4000-300)
RA: 2000
LL: 3000
RL:3000
Some damage is done but not that much. In both cases your human body remains untouched.
P.S. I don't really care what "typical game systems" do, I've read about 70 in the past year and none of them do firefighting combat in a particularly interesting way.