Seriously, yes, a proper barrel roll can be flown within the structural limits of most aircraft.
In fact, a proper barrel roll can be flown practically at +1g. N.Sattarov, a Russian test pilot, won a bet that he'd roll a Tupolev 154 (a 160-seat airliner) so the people inside wouldn't notice it without looking out the window. It was considered a grave violation and cost him a place in the space crew, but that's another story.