Abstract: This inspection device includes an open ended, elongated sighting tube with an optical inspection window in the outer circumference for binocular viewing of the chamber. The elongated sighting tube is generally cylindrical and has a relatively short dimension of between about 1? and 2? and the sighting tube has a longitudinal axis which coincides with the longitudinal centerline of the gun barrel when the gun barrel inspection device is placed into position in the breech. A substantially circular angled specular flat plate mirror of a relatively thin dimension of from about 1/32? to about 3/32? is attached with the tube to an angled back plate plug that terminates in a substantially circular angled flat surface to receive and support the angled mirror. The back plate plug is sized to be inserted into the open end of the elongated sighting tube to position the angled mirror in a supported arrangement within full view in the optical inspection window.