Yes, for the sole purpose of repair and subsequent return to its owner. It is suggested that the owner obtain permission from ATF for the transfer by completing and mailing ATF Form 5 (5320.5) to the NFA Branch and receive approval prior to the delivery. The gunsmith should do the same prior to returning the firearm.
Only the face of the form needs to be completed in each instance. ATF Forms 5 may be obtained from the Bureau of ATF, NFA Branch. ATF Form 5 is also available on the internet at www.atf.gov