Muzzle-loading rifle, which comprises a breech plug (1) and a barrel (2), both fixed in a connection area (3), characterized in that the breech plug (1) is provided with a continuous flange (11) that presses from inside against a seating surface (12) of the barrel (2) when the breech plug (1) is fitted in the interior of the barrel (2), so that said pressure increases when the powder (7) explodes on the second end (5) of the breech plug (1). As a result, the seal between the breech plug (1) and the barrel (2) is strengthened and the gunpowder is prevented from reaching the connection area (3), thereby making it easier to detach the breech plug (1).