The pellet bow is the longbow version of a slingshot. I’m not really sure how to build it otherwise though.
Help me with it please.
I'd say a pellet bow is at best a shortbow version of a slingshot.
AD&D has stats for a pellet bow in
Oriental Adventures, but offhand I can't think of official 3E stats for them.
The simple approach is just use the damage and ammunition cost of a sling — they ought to be able to use stones or bullets plus the other stats for a Shortbow.
The weapon stats would be something like this:
Martial Weapon (Ranged Weapon)
Pellet Bow; 30 gp; 60 ft. range increment; 2 lb. weight.
Bullets [for 10]: 1 sp; 1d4×2 bludgeoning; 5 lb.
Stones [for 10]: cost n/a; 1d3×2 bludgeoning; 5 lb.;
–1 attack penalty
Pellet Bow
You need at least two hands to use a pellet bow, regardless of its size. You can use a pellet bow while mounted. If you have a penalty for low Strength, apply it to damage rolls when you use a shortbow.
You can hurl ordinary stones with a pellet bow, but stones are not as dense or as round as bullets. Thus, such an attack deals damage as if the weapon were designed for a creature one size category smaller than you and you take a -1 penalty on attack rolls.
…
That makes it a really crummy weapon, but they
are really crummy weapons.