It was commonly believed that the longer the barrel, the "harder" the gun shot. And there was some truth in that. All things being equal, a longer barrel would produce slightly higher velocity, but more noticeably, would throw a tighter pattern of shot. Smokeless powder and refined choke tubes make it possible today to get very tight shot patterns with barrels as short as 20". In the days before choke boring the best work was done with a very long barrel which extracted all the energy from the powder. The long barrel allowed the gas pressure to drop so that the wads were not driven into the shot column as it left the barrel.
W.W. Greener is generally credited with perfecting the choke bored barrel in the 1870's. Greener's guns shot patterns which were absolutely unbelievable at the time. He showed that even with black powder, properly choked shotgun barrels could be made as short as 25" and still be more deadly than cylinder bores of any length. Without choke however, the best patterns come from long barrels.
