A stonebow, or bullet crossbow, resembles a light crossbow except for the distinct U-shaped bend in the stock.
Instead of bolts, the stonebow shoots sling bullets. The bow has two strings with a leather pocket between them to hold the bullet.
Loading: Loading a stonebow is a move action (a free action if you have the Rapid Reload feat) that provokes attacks of opportunity.
Firing: You can shoot, but not load, a stonebow with one hand, but doing so imposes a –2 penalty on your attack rolls. You can shoot a stonebow with each hand, but you take a penalty on attack rolls as if attacking with two light weapons. This penalty is cumulative with the penalty for firing one-handed.
You can shoot ordinary stones with a stonebow, but stones aren’t as dense or as round as bullets. When using stones, you take a –1 penalty on attack rolls and deal damage as if the weapon were designed for a creature one size category smaller than you.