California game wardens have no field device to check lead content of a bullet at this time. If the warden is determined to check the metallurgical make up of the bullet you are using they will have to retrieve the bullet from the kill, or get one from you for testing.
I can’t imagine anybody that values their guns using iron bullets, but iron bullets wouldn’t be nearly the fire hazard some patching material, or some patch lubes, or just big fat charges of powder that don’t burn completely in the barrel, would be.
Hungry Horse