Uncle Hans does good work, and I don't want to take anything away from him. But you don't need a Vang Comp barrel, really. Any barrel on a house gun here at Casa Lapin- all of them straight from the factory plain jane 18- 20" Remington barrels- will shoot plenty tight patterns with Federal buckshot loaded with FliteControl wads. And they cost from $70 used to $140 new (with factory rifle type night sights on the new ones no less).
I went through a phase once of trying to get buckshot to pattern better at longer ranges, and was having choke tubes put in, forcing cones extended and all that jazz. Guess what- just buy the right ammo these days and forget about altering the barrel's internal geometry. You'll likely get tight patterns. My favorite house gun has an old Police gun 18" CYL bore barrel, and shoots 4" patterns with Federal LE 127-00 at 25 yards.
fwiw,
lpl