Chokebore

n. 1. In a shotgun, a bore which is tapered to a slightly smaller diameter at a short distance (usually 21/2 to 3 inches) to the rear of the muzzle, in order to prevent the rapid dispersion of the shot. [ Webster 1913 Suppl. ]

2. A shotgun that is made with such a bore. [ Webster 1913 Suppl. ]