Armoured mages
By Chris Lea
In case anyone's interested, here's my system (it's still being tweaked somewhat):
In order to cast a spell while in armour, a mage must make a save vs. spells, with the following modifiers to the roll:
-1/10# of armour worn (or portion thereof)
-1 armour is "fairly bulky"
-2 armour is "bulky"
-2 (-5 for illusion spells) if wearing visored helm
-1 if wearing leather gloves
-2 if wearing metal gauntlets
-1 (-2 if somatic component) for small shield or buckler
-2 (-4 if somatic component) for large shield
-1 spell to be cast is from level 1 or 2
-2 spell to be cast is from level 3 or 4
-3 spell to be cast is from level 5 or 6
-4 spell to be cast is from level 7 or 8
-5 spell to be cast is level 9
+5 caster is elf
+3 caster is gnome
+2 caster is half-elf
+3/proficiency slot used to facilitate casting
If roll is failed, the spell is lost from memory. On a natural "1" some nasty magical disaster might happen.
For convenience: banded -6; bronze plate -7; chain mail -4; elfin chain -2; leather -2; padded -2; plate mail -7; ring mail -4; scale mail -5; splint mail -6; studded leather -3; field plate -11 (-14 for illusions) [includes visored helm & gauntlet mods]; full plate -12 (-15 for illusions) [includes visored helm & gauntlet mods]
So an elven fighter/magic-user (3/3) wearing chain mail with small shield and leather gloves tries to cast a magic missile. The following modifiers apply:
-4(chain mail)-2(shield)-1(gloves)-1(lvl 1 spell)+5(is elf) = -3 .
He will succeed on 15 or better on d20.
If he drops the shield and gloves, it's a 12 or better roll.
A 23rd level human mage in splint mail with a ring of protection +2, who has used one proficiency slot to aid casting in armour attempts to cast a limited wish.
-6(splint mail)-4(level 7 spell)+2(ring)+3(proficiency)=-5
He will succeed on a 9 or better.
It is suggested that the player who wants to do this, do the math himself