As mentioned by KurtL, the only interchangeability is within platforms.
A Contender barrel will fit any Contender frame, whether it is an early generation frame or later generation, easy open, frame, or the latest Generation 2 (G2) Contender frame. The only exception here is the Armor Alloy barrels will only fit Armor Alloy frames, unless they are modified to fit.
Encore barrels will all fit Encore frames whether they are "Pro Hunter" frames or "Endeavor" frames or the standard Encore frame (they are all "Encore" frames...).
There is no barrel interchangeability between the Encore or Contender.