I'm waiting on a Form 1 to come back for a SBR.  I am planning to send the receiver to a builder in another state when the Form 1 comes back.  Do I need an approved 5320.20 before shipping the receiver to the builder?

No,  Shipping an NFA firearm to a gunsmith for repair does not require any paperwork.  They used to require a Form 5 for the temporary transfer to the gunsmith, but now it's not a requirement.

I have heard though that a "letter of intent" is nice which identifies the NFA piece and states a general timeframe on the repair process. In case the builder is audited, it may make it a tad easier to explain a device that is not registered to the builder.

I just found this in the National Firearms Act Handbook:

9.5.1 Repair of firearms. ATF does not consider the temporary conveyance of an NFA firearm to an FFL for repair to be a “transfer” under the NFA. Thus, a transfer application is not required to convey the firearm for repair or to return the repaired firearm to its owner/possessor. Nevertheless, in order to avoid any appearance that a “transfer” has taken place, ATF recommends that a Form 5 application be submitted for approval prior to conveying the firearm for repair. It is also recommended that the FFL making repairs obtain an approved Form 5 to return a repaired firearm. If Forms 5 are not used to convey a firearm for repair or return the repaired firearm to the owner, the parties should maintain documentation showing that the conveyance was for purposes of repair, identifying the firearm, and showing the anticipated time for repair. Approved Forms 5, or the recommended documentation, will show that an unlawful “transfer” did not take place and that the FFL making the repairs is not in unlawful possession of the firearm. A non-FFL who proposes to transport a destructive device, machinegun, or short-barrel shotgun or rifle interstate to an FFL for repair should first obtain an approved ATF Form 5320.20 before transporting the firearm. www.atf.gov/firearms/nfa/nfa_handbook/0607nfa_handbook-rev.pdf

So it sounds like I should get a 5320.20 first.  So I would list repair as the reason for transportation, and FedEx or UPS as the mode of transportation?

Quoted: I just found this in the National Firearms Act Handbook: 9.5.1 Repair of firearms. ATF does not consider the temporary conveyance of an NFA firearm to an FFL for repair to be a “transfer” under the NFA. Thus, a transfer application is not required to convey the firearm for repair or to return the repaired firearm to its owner/possessor. Nevertheless, in order to avoid any appearance that a “transfer” has taken place, ATF recommends that a Form 5 application be submitted for approval prior to conveying the firearm for repair. It is also recommended that the FFL making repairs obtain an approved Form 5 to return a repaired firearm. If Forms 5 are not used to convey a firearm for repair or return the repaired firearm to the owner, the parties should maintain documentation showing that the conveyance was for purposes of repair, identifying the firearm, and showing the anticipated time for repair. Approved Forms 5, or the recommended documentation, will show that an unlawful “transfer” did not take place and that the FFL making the repairs is not in unlawful possession of the firearm. A non-FFL who proposes to transport a destructive device, machinegun, or short-barrel shotgun or rifle interstate to an FFL for repair should first obtain an approved ATF Form 5320.20 before transporting the firearm. www.atf.gov/firearms/nfa/nfa_handbook/0607nfa_handbook-rev.pdf So it sounds like I should get a 5320.20 first.  So I would list repair as the reason for transportation, and FedEx or UPS as the mode of transportation?

"Transport" means you are physically taking the firearm yourself.  "Shipping" is not the same thing.  You can do a Form 5, but it's not necessary.

Ask the gunsmith you're sending it to what he wants.  Some still like the 5320.20 form to accompany the weapon.

Quoted: Ask the gunsmith you're sending it to what he wants.  Some still like the 5320.20 form to accompany the weapon.

It's a Form 5 guys.  Only the Form 5 covers the transfer of possession that takes place.  NFA Branch has already relaxed this as a requirement for gunsmithing/repair since the gunsmith's license technically covers the possession issue.

But despite being the wrong form entirely, the 5320 doesn't cover the temporary transfer of possession of the NFA firearm to another individual or party.

The 5320 covers the physical transport by the owner/legal custodian interstate, i.e. taking it with you when you travel outside your own state of residence.  There is no approval for the transfer of possession of the weapon stated or implied in a 5320.

Wrong form entirely.  No different than submitting a Form 1 to buy an NFA firearm.

Okay, a copy of the Form 1 and a letter it is then.  

Quoted: Quoted: Ask the gunsmith you're sending it to what he wants.  Some still like the 5320.20 form to accompany the weapon. It's a Form 5 guys.  Only the Form 5 covers the transfer of possession that takes place.  NFA Branch has already relaxed this as a requirement for gunsmithing/repair since the gunsmith's license technically covers the possession issue. But despite being the wrong form entirely, the 5320 doesn't cover the temporary transfer of possession of the NFA firearm to another individual or party. The 5320 covers the physical transport by the owner/legal custodian interstate, i.e. taking it with you when you travel outside your own state of residence.  There is no approval for the transfer of possession of the weapon stated or implied in a 5320. Wrong form entirely.  No different than submitting a Form 1 to buy an NFA firearm.

Yep, I had the number wrong for sure.  And you're correct that the NFA Branch has relaxed the requirement, hence the "recommended" wording, rather than "required."

But the fact remains that some gunsmiths want the Form 5 anyway (it IS optional, after all), so if you want them to do the work you get the Form 5 completed.  THAT is what I was getting at, I just got the form wrong.  My gunsmith didn't require one so I didn't bother.