Don't believe everything you read!

The barrel-group should have parallel chambers, perpendicular to the breech-face, and the tubes should curve inwards at some point well forward of the chambers. xs hints at this in his post. A pair of barrels will rarely, if ever, have straight-tapered converging bore centre-lines all the way from the breech-face, although in the 150 years of cartridge double guns across several continents, anything is possible!