I have a 1999 Verney-Carron catalog, in which they describe their "Grand Becassier" model (probably best translated as "Woodcock Special" in English). Here's how they describe the bottom barrel (it's an OU):

"Tube inferieur raye dispersant". In this case, the "dispersant" makes the purpose of the barrel very clear--even if it weren't on a "Woodcock Special".