Mehul. No they weren`t ( a minor consequence perhaps. )
A straight grip facilitates easier and faster handling of a gun for bird shooting ( particularly ) - `snap` shooting if you prefer.
A `Pigeon` ( more accurately `live pigeon`, to differentiate from `clay pigeon` ) gun has extra weight, a raised rib and a `Prince of Wales` or full pistol grip to reduce recoil and steady the gun because it was pre-mounted - a trap gun in other words. A `pigeon gun` with three inch chambers isn`t a pigeon gun, it`s a wildfowler.
I can`t say that I fancy shooting a heavy calibre double rifle without a pistol grip.............( and I don`t believe that Buffalo are trained to respond to the command `pull` ! )