Rei's suggestion with 'you = player' and 'IGNORE_YOU' is the common way to avoid collision with the origin of the bullet.

But, if this doesn't work, you could try this:
You could create the bullet at a vertex at the gun's end with vec_for_vertex.
Then you could reduce the collision box of the player with max_x, min_x, max_y, min_y, that the gun's end is out side that collision box, and the bullet is created outside.
You can see the size of the box when hitting F11 twice.

About "you = player" and "you = ent_create":
you and me are pointers that are relatively to an entity's function, this means that the 'you' within the function of the player points at a different entity than the 'you' within the bullet's function.