free-bored
[ free-bawrd, -bohrd ]
/ ˈfriˈbɔrd, -ˈboʊrd /
adjective
(of a rifle) having a bore that is not rifled within a short distance of the breech, so that a fired cartridge travels about 1/2 inch (1.3 cm) before being engaged by the lands, thus reducing initial high pressures.