Telescope-like bore
internal diameter, composed of downwards (i.e. counting from the stock) "step-by-step" increasingly cylindrical sections
Télescopique (Perce ~); Teleskopisch (i.e. "Teleskopische" Bohrung); Telescópica (Sección ~).
Identical types: 4➺ Cylindrical.
Internal diameter with the shape of a "telescope-like" cone (➺ Italian Mancina & Fischietto, Macedonian Surla, and Serbian Bas).