For many situations, you probably don't care about the damage done to armor so much as the damage done to the armored object. This system seems, on the surface, to require a multi-stepped calculation to get to the numbers you really want. Fortunately, a little bit of algebraic manipulation shows us that the system is very flexible in cutting through to the desired result.

Imagine that I am wearing body armor, and someone fires a bullet at me. The bullet penetrates my chestplate and chest, lodging in the wall behind me. The damage done to the armor's chestplate is:

Damage_{armor} = ( PR_{armor} / PV_{bullet}
) * ( Unmod Dam )

The bullet now acts like it does damage: { Unmod Dam - Damage_{armor} } and has PV: { PV_{bullet}
- PR_{armor} }. It does damage to me:

Damage_{me} = ( PR_{me} / { PV_{bullet}
- PR_{armor} } ) * { Unmod Dam
- Damage_{armor} }

Damage_{me} = ( PR_{me}
/ { PV_{bullet} - PR_{armor}
} ) * { Unmod Dam - ( PR_{armor}
/ PV_{bullet} ) * ( Unmod Dam
) }

Damage_{me} = ( PR_{me}
/ { PV_{bullet} - PR_{armor}
} ) * { 1 - ( PR_{armor} / PV_{bullet}
) }* ( Unmod Dam )

Damage_{me} = ( PR_{me}
/ { PV_{bullet} - PR_{armor}
} ) * { ( PV_{bullet} - PR_{armor}
) / PV_{bullet} } * ( Unmod Dam
)

Damage_{me} = ( PR_{me}
/ PV_{bullet} ) * { ( PV_{bullet}
- PR_{armor} ) / ( PV_{bullet}
- PR_{armor} ) } * ( Unmod Dam
)

Damage_{me} = ( PR_{me}
/ PV_{bullet} ) * { 1 / 1 } * ( Unmod
Dam )

Damage_{me} = ( PR_{me} / PV_{bullet}
) * ( Unmod Dam )

The damage applied to me is just as easy to determine without ever performing the intermediate steps. This shortcut will be very useful for determing damage in situations where the weapons are far more damaging than the targets. For example, if a very penetrating round (like that fired from an MD weapon) is fired through a wall, body armor, and a person, with still enough PV to carry through the person, we can easily determine the damage done to the person without following the bullet through the wall and the armor.

The shortcut that is presented here: A GM or player adds up the PR of whatever objects a round is being fired through, and as long as the round will strike the intended target he doesn't need to keep track of the damage done to the intermediate objects.

One complication: Bullets often have enough PV to penetrate body armor, but will then stop in the body. Remember that the effective PR of 4 for a human body is only intended to tell us when a round will pass through the person, doing damage on the other side. If this shortcut is employed you must use, rather than the PR: 4 for a human body, the effective PV of the bullet when it reaches the body. If it has an effective PV of 3, it won't penetrate through the body. Using the full PR of 4 will inappropriately inflate the damage, in this case by 25%.