A bolt locking housing (16) on a gun, behind the chamber (4) thereof, for receiving a bolt (6) including an extractor (10) having an extractor hook that grips a corresponding extractor groove (21) of a cartridge (2) within said chamber (4), characterized by said bolt locking housing (16) being asymmetrically machined internally, such that there is provided at least a first protrusion (18) that becomes co-aligned with and serves to support head of extractor (10), when bolt (6) is fully closed and lugs (7) thereon are interlocked into bolt locking housing (16), thereby preventing deformation of casing of said cartridge (2) after detonation.