To provide a rifle and shot gun having a barrel with a chamber capable of realizing a sure and smooth charging and a magazine, in a rifle or shot gun using a slender cartridge of No.410 aperture in which the ratio of the cartridge outer diameter to the outer diameter of a rim is large, and a rimmed cartridge of another aperture of the same type.

In this rifle or shot gun, a circular guide chamfered cutout 12b is formed in substantially the whole lower half part of a guide chamfered cutout opening 12a or in a part of the lower half part of a rim contact surface 12 of a barrel chamber 10.