Choke in a barrel most often results in a thicker wall. About the only exception to this would be if the barrel were first made as a cylinder then the outside "Swaged" down to produce the choke. This is sometimes encountered in cheap single barrels, but not commonly in a double. It is in fact rather common to find the OD of a barrel being beefed up a bit as the choke is approached from what it was a bit behind the choke.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra