Form Factor
A number expressing how a bullet's drag compares to the standard projectile of a chosen drag model, where lower means more efficient.
The form factor is the ratio of a real bullet’s drag to the drag of the reference projectile in a given drag model. A value of 1.0 means the bullet sheds velocity exactly like the standard shape, while a lower number means it is sleeker and more efficient. This ratio is the bridge between a bullet’s physical shape and its ballistic coefficient.
Form factor is also why the choice of model matters so much. A long boat-tail match bullet posts a form factor near 1.0 against the G7 model because the reference is similar, yet a much higher value against G1. Comparing form factors only makes sense when both bullets are measured against the same standard.