There are other ways:
1. Write all your the actors to the collision layer. If they can only shoot each other, they don't need to read collisions (unless you do movement collision checks in the same step)
2. For all bullets, only read the collision. As bullets most likely can't collide with others, writing them to collision layer will only make collision slower. Now with the read collisions, you can do whatever you want.
3. I would use 2 layers. 1 for enemy and one for you. This way, your bullets only check with enemies and enemy bullets only check with your player. Will greatly speed up the collisions for all enemies (especially if you have situations where you go against enemy masses)
1. Write all your the actors to the collision layer. If they can only shoot each other, they don't need to read collisions (unless you do movement collision checks in the same step)
2. For all bullets, only read the collision. As bullets most likely can't collide with others, writing them to collision layer will only make collision slower. Now with the read collisions, you can do whatever you want.
3. I would use 2 layers. 1 for enemy and one for you. This way, your bullets only check with enemies and enemy bullets only check with your player. Will greatly speed up the collisions for all enemies (especially if you have situations where you go against enemy masses)