Honestly you don't need an FFL or manufacturors license to make parts like bolt handles, triggers, or other mods. You just can't install them on the "firearm". If the part isn't regulated by the ATF they don't care. If you needed a license to make a part then everybody who sold them would need one as well. You just can't take a firearm into your possession to install the mod. Now that does not speak to business concerns. There could be some liability involved and you might be required to get a business license depending on your local law or sales volume. If you were doing a lot of this it might be worth looking into something like an LLC to protect your personal assets. That of course is all up to you. Love the jig and the outcome you are getting. As a complete unit those have come out really clean. Great job!