Just to be perfectly clear for the OP ... there is a great flow chart on either CalGuns or the CRPA site. But at a minimum, if you go with a bullet-button, you MUST NEVER put a magazine in that build that has more than a 10 round capacity ... that pops it right back into the AW category. Please read up on the law so that you can eloquently educate people (e.g. LEOs) that ask you about your new purchase.
Normally I sign off with a Stay safe ... but in this case I will go with "Stay out of trouble!!"