Tax permits are generally state and local gov't req'mts.
The 'loophole' for your brother-in-law to make a stock for you is the legal ability to "loan" a gun to someone. Even California has allowance for loaning a gun. Nobody in the gov't is in the business of chasing down some hobbyist that makes stocks for a couple people a yr. Now that same guy puts an advertisement out there and starts turning a significant number of stocks a year for money and that becomes a different story. In Calif, it reqs a business license, a Certificate of Eligibility, a tax number, and finally an FFL.
BTW, I've searched the federal regs and nowhere does it require " a signed copy of an FFL". It simply requires that the recipient of a shipped gun either be legally eligeable to receive the gun (owns the gun, etc.) or be a FFL holder. How all this is determined is on the shipper to determine. ATF has ruled that a fax is now acceptable means, and they also have a website they say is acceptable means of verification. Hell, if you know the guy and he gives you his FFL number on the phone, you can ship it as long as he actually has one. The proof of the recipient having an FFL will come out in an investigation. You don't need to have any evidence as a private citizen and a FFL holder only needs the recipient's FFL number in his bound book. The methods of verifying someone has a FFL are only some means they have deemed that you did due diligence in trying to obtain verification that the recipient had an FFL. What? you expect Remington to send you a copy signed by someone? ROTFALMAO Prior to the web listing of FFLs, the name manufacturers status of their FFL was virtually unknown. But, nobody I'm aware of got in trouble for sending Remington, Winchester, CSM, etc. their guns.
