3.P Gameplay House Rules+Damage Reduction changes

Damage Reduction mostly works as normal with a few changes:

• Weapon enhancement bonuses do not automatically overcome damage reduction.  For example, a good-aligned weapon can overcome DR/evil but an otherwise +5 weapon cannot.
• Damage Reduction is effectively doubled against swarms, mobs, troops, or similar collections of enemies.  For example, DR 5/slashing becomes DR 10/slashing against a swarm's attack.
• Armor and shields grant bonus damage reduction equal to half their AC bonus (after enchantments, round down).  This is similar to the Armor as Damage Reduction rules, but all other statistics of the armor/shield and AC rules remain unchanged.  This DR stacks with any other DR the character may have, and counts as DR/- otherwise.  For example, a character with DR 5/magic wearing full plate and a heavy shield would have DR 10/magic and DR 5/-.  Bracers of armor, shield spells, and other sources of AC that aren't actual armor or shields don't provide this bonus DR.