Maybe I have misunderstood some of the descriptions here, but it appears to me there is some variation in what exactly a barrel roll is.
This is how it was described to me by my RAF instructor, admittedly a long time ago, so it might have changed
Commence at A with wings level on the horizon, pulling up and rolling right to have 90 degrees of bank at B, inverted as we pass through the horizon at C, 90 degrees of bank at D, and recover back at A.
