A person lives in a state where private transfer of firearms requires going to an ffl.
Firearm transfer between residents of different states require an ffl in receiver's state, always, federally.
Would residents of the same state be breaking any laws if they completed a private sale in a neighboring state that neither party is a resident of?

"Meet you at the Home Depot lot just across the border"

They wouldn't be breaking their home state's laws as they weren't even in their jurisdiction, it is legal in the state the transfer takes place and legal federally.  What am I missing?

Question in similar vein.  Private transfers between family members are still legal in my state.  Shipping a firearm between residents of the same state is legal.  Farther goes on business trip, doesn't bring carry gun, nor does he ship it to himself ahead of time.  Trip gets extended now wants gun.  May I ship him one of my guns directly or one of his?  It would not be a transfer between residents of different states, but it would not be taking place in the home state.

Sounds like you're gonna get burned.  Better to back away and leave that alone.

Both are no.

The first because it's an out of state sale and it's only legal under Federal law if is (1) legal both in that state and the buyer's state of residency and (2) is done through an FFL (and (3) a long gun.

The second because (Federally) you can ship a gun to yourself out of state (and only to yourself).   If you ship a gun to someone else, that's no you.  If someone ships you a gun, it's not you.  As described, assuming no contravening state laws forbidding it, the gun would have to go to an FFL and be transferred.

Nobody is getting burned, just want to buy a gun from a long time friend, and save the 35 bucks transfer.  We live right on the border.  But given our jobs we also don't want to break any laws.

best spend the extra 35 bucks, sure beats a shit ton in legal fees

in 27 cfr 478.29 it says

You can't bring a gun back into your home state that you acquired in another state, unless inheritance, a rifle or a shotgun you bought at a dealer or in compliance with 478.30

478.30 says

You can't give a gun to a resident of a different state unless inheritance or loan

So it seems like if you are in compliance with 478.30, 478.29 doesn't apply.

the second question is a little harder as 478.29 appears to apply to bringing a gun back to your state of residence you acquired outside of it.

you are incorrect about shipping.  From atf faq.

You are right of course and this is probably more academic then anything, but who doesn't love a good loophole?  That is how we got "firearms," pistol braces, and binary triggers.

There's a ton of misdirection in your answers to your own questions which never mentioned transferring through an FFL.

No as the buyer would be acquiring a gun in a state he is not a resident of.

Honestly, this might seem like an enticing idea, but alas it is nothing more than another really *bad* idea for a loophole in order to sideskirt federal regulations...

And as others have already pointed out, this idea likely falls off its hinge on the premise that neither of you are residents of the state where the transfer is to take place.

I'd re-read those relevant clauses and definitions of the GCA, because state residency is likely part of the definition of the 'persons' verbiage as employed in the letter of the law.