The guns with the rifled dispersion barrels are made with European woodcock hunting in mind. Verney-Carron offers one (an OU), as does Beretta. They're usually short barreled and very light, and the other barrel in the newer ones often has choke tubes.

I saw a Manufrance Robust set up with a canon raye dispersant. Would've bought it just to give it a try, but the seller was way high in my way of thinking.