That is incorrect. For the barrels to "run parallel" at the last few inches they would have to be bent substantially at some point back. By looking down the bores from the breech ends you can see concentric rings that are clearly aligned equally on all sides. Were the barrels bent, in order for them to become parallel, the rings would not be concentric at that point (in the bend).
What you are seeing from the outside, that makes it look that way, is the way the barrels are struck. Usually, with better guns especially, the barrels are thinner just behind the choke, the the walls thicken slightly through the choke area and at the muzzles. This is a result of sriking (filing) done to create the right handling characteristics, and also to protect the muzzles by having a little more metal there.
SRH
