Ok then, I'll think of some ammo types.

Poison Dipped Bullets: when a player is hit, they have a 40% chance of getting poisoned. The "bleeding" damage or red gas harms players.

Tumbling Bullets: bullets that rotate in the air as they travel. This would be a 40% chance for +1 damage for one bullet fired.

Chocolate Bullets: bullets made out of chocolate that heal gang members. Heals 3 hp per bullet. (Yes, like the muffin cannon.)

Sticky Bullets: bullets covered in a sticky gelatin. The bullet causes players to loose their ability to switch weapons or use items (grenades, food, etc.); 40% chance.