this link seems to describe a barrel roll as I understand it:
Barrel roll - Wikipedia, the free encyclopedia
not that wikipedia is the ultimate authority out there, but it does have the benefit of being correctable if someone believes they can describe the manoevure better.
the CAA makes the point that barrel rolls and other manoevures flown at low level can be potential killers:
http://www.caa.co.uk/docs/33/CivilAi...eforPilots.pdf
not that I am an expert in these matters - and there are people posting on this thread with far more experience than Lighting Mate gives them credit for, including (ex) RAF display pilots....but the crucial part of the manoevure IMHO is to go through the gate correctly. If you don't see what you expect in terms of the numbers, your energy and attitude, then you need to start thinking safety first rather than completing the manoevure.