In California, if the material used is approved, (of which bismuth and tin most definitely are) I see no problem making your own and using them. Ultimately is the burden of the Department of Fish and Wildlife to prove that your projectile is made of a banned material (lead), and they have ways of testing it even in the field. Its really not that difficult. There are pre-made options on the market as well that will work--albeit not as good as lead.