The kind of loan that's not a transfer under federal law would be a really short-term loan where the person loaning the gun has supervision over the person borrowing it. Such as:
(1) renting a gun at a shooting range
(2) renting or borrowing a gun from a professional guide on a guided hunting trip.
(3) loaning a gun to a hunting buddy who brought his own gun, but now finds it out of commission or unsuitable for the conditions of the hunt, when you're both out of state or are residents of different states, but hunting together on the same property that day.
(1) renting a gun at a shooting range
(2) renting or borrowing a gun from a professional guide on a guided hunting trip.
(3) loaning a gun to a hunting buddy who brought his own gun, but now finds it out of commission or unsuitable for the conditions of the hunt, when you're both out of state or are residents of different states, but hunting together on the same property that day.