In a D&D world, one where gunpowder and steamworks also exist, the previous balance is upset. Normally Psi & Magery used to exist despite each, and their effects whizzed right past each other.
When times change, and guns are invented, and steam-cannons tear down mystic force fields,
Now a triune disharmony unfolds, a rock-scissors-paper balancing, if you will.
Psychics can now pinpoint and disrupt magical effects with relative ease, yet they find that the price of this is that mystic metals, such as cold iron, mithril, adamant, etc can shield and even proof targets against their mental abilities.
Sorcerors can easily upset the apple carts of those who rely on their guns, steamjacks, and other war-engines. However, psychics can pick apart their magic with facility.
Metal Dampens Psionics:
Every plus of a carried metal item, such as a +2 mithril sheild, or a +3 cold iron longsword,
counts as one-and-a-half plusses to add to the saving throws (if allowed) versus psychic effects launched at the target. And if no psychic save is permitted, still half the plusses carried counts as psychic resistance for the target.
So, Jamal the Fighter has a +2 cold iron hauberk, and a +2 mithril longsword. His +1 steel crossbow bolts do not count since they are mundane metal. Jamal gets +6 on his Will save versus Psionic Charm.When Jamal gets hit by Psychometabolic Hammer, he has no save, but counts as having power resist 12.
If a power allows both save and resist, he only gets the save.
Psionics Pierce Magic:
Dispel Magic etc. do not affect psychic powers unless activated via a metal focus, such as a staff of cold iron, or a mithril wand. This will at a minimum triple the cost of the item. Psychic defenses count as 150% versus magic, so if a psychic manifest Empty Mind, he gets +2 versus pychic attack, but +3 versus magic charm, for example. If a target gains power resistance from a magical source, a manifester is +2 on his level check. Power Resistance also provide Magic Resistance of 2/3rds value. so PR31 = SR20.
Magic Divides Metallurgy:
Dispel Magic can sabotage the working of Gunpowder, Dweonetics, Computers, Robots, etc.
Magic Resistance can shed off powers such as lightning guns, stun guns, concussion grenades that come from a techno weapon.