There are dozens of different types of bullets, each with their own purpose and unique identifiers.
These bullets are the size of Basic's bullet, and have similar characteristics. Some bullets are faster than others, and some are stronger. Most bullet tanks use this bullet.
These bullets are somewhat weaker and slower than basic bullets, and also have more spread. Most bullets are the same speed, but some branches have faster or slower bullets. Most of the Pelleter branch uses this.
These bullets all have the basic g.pound stat, with other stats added to them. These bullets are larger and stronger than Basic's, and some of them can instantly kill glass builds.
These bullets increase in size over time, and are unique to the Mini Grower branch. The larger the bullet, the more damage it does.
These bullets have tiny auto-turrets on top of them that fire bullets themselves. These bullets are weaker than Basic (though they may look the same size). The auto-turret bullets are weak by themselves but can stack up damage over time.
These bullets are small, but they can pack a huge punch if many are together. They have increased penetration and can predict the movement of an opponent, making it difficult to fight. These are prevalent (and come in different sizes) in Auto-2 and Auto-Basic branch.
These bullets are much larger than Pounder, and have g.destroy as their main stat. These all branch from Destroyer. A subset of these is g.anni, which have even larger bullets at the cost of a little penetration and speed. The damage increases if you are going toward your target and decreases if you are going away from your target.
These bullets are faster and have more recoil than Destroyer, though give the same damage. However, they have less reload for balancing. They have a small hole in the center that indicates their less weight (and thus more speed)
These bullets are tiny and fast.
These bullets speed up over time.
These bullets grow larger over time, but speed up and deal more damage if you are moving forward.
These bullets are thin and deal little damage, but are fired at an extreme rate.
These bullets are not fired per se, but are produced from the death of a Shrapnel Nuke or Zeppelin Bullet.