Damage Resistance Modifier

Damage Resistance Modifier on ammunition in Fallout and Fallout 2, known as Penetration in Fallout Tactics, indicates how much to change the target's damage resistance. In Fallout and Fallout 2, a lower amount indicates higher damage. In Fallout Tactics, the opposite is true.

It does not work in Fallout due to engine bugs.

So for example, a 10mm JHP in Fallout 2 when examined reveals that it has a "DR mod" of 25. This means that against an enemy with DR 0, they would instead have DR 25 against any attack with that ammo. In this case, this ammunition also has a Damage Modifier of 2, which makes this ammo appropriate only for low-DR targets.

In Fallout Tactics, a hypothetical ammo with Penetration 25 would operate in the reverse: an enemy with DR 25 would instead have DR 0.