ignore collision question

I am trying to get a projectile with a rigidbody to collide with a box with a rigidbody.

after the projectile collides with the box, I need the projectile to instantiate itself in the direction of the normal of the box.

I need the new instantiated projectile to ignore all collisions with the box it collided with, but be able to collide with the other boxes in the same layer!

unfortunately once the projectile instantiates it collides with the box again. I wanted to try using physics.IgnoreCollision(collider, other.contacts[0].collider); this way the projectile will ignore the first object it comes in contact with.

it says that IgnoreCollision can't reference the same two shapes however? can someone help lol