Fixed Cannon (3.5e Equipment)
From D&D Wiki
These massive cannons are meant for nothing more then tower defense, as they completely stationary when in use because they are way too big for a single creature to carry, and the recoil from the blast who shatter the bones of someone trying to carry it. They use 5lbs of gunpowder per load and take a full round to load. This does not provoke an attack of opportunity because under no condition who you be using one at close range (unless an enemy is within range to make a ranged attack). The only difference between a small, medium, and large fixed cannon is the barrel size, which with a longer barrel puts a better back spin on the cannon ball, increasing damage.
Set Up: They take 7 hours to set up from scratch (once purchased) and 5 minutes to clean after each battle. After 15 shots, soot and grime can clog the barrel, giving it a 10% chance for shot failure, dealing 2d6 back fire damage. Add an extra d6 per 15 shot fired without cleaning.
Ammo Information: Cannon balls all cost 50 gp for per, and gun powder costs 30 gp per 5lbs. It takes 80 gp to fire this cannon once.