the image of the bullet is transparent, yes i have tested the hitboxes https://www.greenfoot.org/scenarios/9908 < here, and the hitbox seems fine to me on the car (that is being shot at) aswell as the bullet.
I dont really understand you problem. But the scenario you are pointing at seems to be broken. Its quite old.
Generally though greenfoot measures collisions al if the actor was as big as the image, no matter if some part is transparent or not. So try using images that don't have big transparent corners or outlines. Otherwise you will have to code your own collision measurement system, for example by using multiple actors to create a more detailed hitbox
the image of the bullet is transparent, yes i have tested the hitboxes https://www.greenfoot.org/scenarios/9908 < here, and the hitbox seems fine to me on the car (that is being shot at) aswell as the bullet.
Do not link someone else's scenario for a problem in one of yours. Provide your code (Bullet and Car classes).