Adding the "BANG!" of gunpowder to TSR's AD&D Battle System, 2nd Edition, is as easy as the following statistics:

Hand Held Weapons (Rate of Fire: One shot every other turn)
Pistol A.D.: 1d6Range: 3" / 5" / 10"
Arquebus A.D.: 1d8Range: 5" / 10" / 20"
Matchlock A.D.: 1d10 Range: 6" / 11" / 21"

Explosive Bombs
Grenades= 1 d8, 1 d6, 1 d4 Range: 2" / 4" / 6"
Petards = 1d12 to 4d12 Range: 1" / 2" / 3"

Big guns	A.D.	Hits	Range	Crew	Rate	Move
Cannonade	1d12	6	6" / 12" / 24"	2	2	6" / 9"
Light Cannon	2d12	8	8" / 15" / 30"	4	2	6" / 9"
Medium Cannon	3d12	10	9" / 18" / 36"	6	3	4" / 6"
Bombard Cannon	4d12	15	11" / 21" / 42"	8	4	3" / 4"

Ranges for Indirect Fire (Takes one turn to change to direct fire)
Cannonade 12" min. / 24" max.
Light Cannon 15" min. / 30" max.
Medium Cannon 18" min. / 36" max.
Bombard Cannon 21" min. /42" max.

Point Costs for Gunpowder Weapons

Guns

Pistol 5 points
Arquebus 7 points
Matchlock 9 points
Cannonade 12 points
Light Cannon 24 points
Medium Cannon 36 points
Bombard Cannon 48 points

Grenades

A.D. 1d4 2 points
A.D. 1d6 4 points
A.D. 1d8 6 points

Petards

A.D. 1d12 10 points
A.D. 2d12 20 points
A.D. 3d12 30 points
A.D. 4d12 40 points