From the "Might Fortress" AD&D2 historical refence book:



Some additional rules apply to the use of gunpowder weapons:



Armor Classes: The great advantage of firearms is their ability to

punch through armor. At short range, all armor is ignored; the target`s

AC depends entirely on his Dexterity and cover. At medium range, the

target`s AC is penalized by 5. At long range, the target`s AC is

penalized by 2.

These penalties apply only to the portion of the character`s AC which

comes from wearing armor. Dexterity bonuses are unaffected. The

penalty cannot make a character`s AC worse than it would be if he was

wearing no armor.

Also note that many things that would stop an arrow will not stop a

bullet, particularly at short range. Characters must get behind more

substantial barricades to qualify for the cover bonus rather than

concealment.



Additional damage: No matter what sort of firearm is being used, any

time a character rolls an 8, 10, or 12, he rolls the die again and adds

the second roll to the first. If the second roll is again an 8, 10, or

12, he rolls a third time, and so on. It is possible for a gun to cause

trememndous damage.



Missing Fire: For various reasons, these firearms would occasionally

fail to fire altogether. If the attack roll is a 1, the weapon misses

fire and does not fire at all. It cannot be fired again until 10 rounds

are spent clearing the charge from the barrel, cleaning, and reloading

the piece.



Hanging Fire: Sometimes the powder in a gun`s breach smoulders

momentarily before igniting. This is called "hanging fire." If the

attack roll is a 2, the weapon hangs fire. On subsequent shots it will

miss fire on a roll of 1 or 2 and hang fire on a roll of 3. Each time

it hangs fire, the chance of missing fire increases by 1. This persists

until the piece is cleaned.



Fouling (optional rule): Every time a gunpowder weapon is fired, burned

powder accumulates in the barrel, priming pan, and touch hole. For

every three shots fired (rounded down), the chance of missing fire

increases by one, just like hanging fire. This persists until the

weapon is cleared.



Point Blank Range: If a musket, arquebus, caliver, or pistol hits a

target that is within 5 feet of the muzzle, the target suffers one

additional point of damage from burns.



--Lord Rahvin