In particular, I'm referring to O/U models with nothing between the barrels except at the end. For example, on a Blaser F3...
http://www.blaser-usa.com/F3-SuperSport.1098.0.html
...you can see there is no ribbing between the barrels. However, on a Winchester Select (my current competition gun)...
http://www.winchesterguns.com/produc...asp?mid=513015
...the barrels are not "floating." The idea of heat dissipation makes the most sense on this question, though I thought I read on the Kolar or Krieghoff sites that "floating" barrels are also supposed to produce more consistent patterns.