I have the latest PDF version of the book. There is a script given for switching guns, that does not allow for switching to the Assault Rifle. I edited my code to allow for it, but others may encounter this issue. Below is what is in the text.
void Update ()
activeWeaponType = Constants.Pistol;
activeWeaponType = Constants.AssaultRifle;
else if (Input.GetKeyDown(“3”))
activeWeaponType = Constants.Shotgun;