Any time a gunsmith takes in work that he can not do "right now", "on the spot", and must be kept over night, must be logged into his 'bound book' as per ATFE regs. (and logged out when it leaves, preferably with the person who left it with you,,, anyone else, his wife, his son,, form 4473 and NICS check). At any point, if you are "in the business", full time, part time, doesn't matter, a FFL is required. Whether you supply the receiver, order for others (or yourself), buy/sell/trade or not,, if you are "in the business" to profit (and with the expense of any and all gunsmithing tools and equipment you can not even do friends guns for free unless you do not value your time at all, and a pat on the back is enough) you are required to be licensed. And, think of this, no FFL, no gunsmith liability insurance. You can not imagine how much information I have been required to supply insurance carriers with (think several pages of policies and procedures for your 'company'), including a copy of my Federal Firearms License, to be covered. Life ain't simple. And then there are sales taxes, state income taxes and the IRS,,, and we still have ITAR even though the White House has changed occupants. Ever wonder why gunsmithing costs what it does? Work on and modify your own, personal firearms and don't worry about it!