You can probably get away with less than +3g doing a `barrel-roll`, starting at 300kts. The trick is to keep a matched pitch and roll rate at all times and keep it balanced.The nose must be above the horizon with wings level as you go inverted, otherwise it will end in tears(in your eyes) and tears in the airframe, unless it is more highly stressed.Bob Hoover does it in a Commander, whilst pouring water into a cup on top of the instrument panel...on a vid, somewhere........Best practised on a suitable aerobatic aircraft first.......!!