chokebore

[chohk-bawr, -bohr] /ˈtʃoʊkˌbɔr, -ˌboʊr/
noun
1.
a bore in a shotgun that narrows toward the muzzle to prevent shot from scattering too widely.
2.
a shotgun with such a bore.
Origin
1870-75; choke + bore1
British Dictionary definitions for chokebore

chokebore

/ˈtʃəʊkˌbɔː/
noun
1.
a shotgun bore that becomes narrower towards the muzzle so that the shot is not scattered
2.
a shotgun having such a bore