A deconfinement device for the casing of a piece of ammunition enclosing an explosive load able to be ignited by a priming fuse, said device comprising a connecting ring linked to the casing and enabling the priming fuse to be joined to said casing, wherein said device incorporates a structure to ensure a weakened and shearable link between said fuse and said connecting ring, said link being sheared further to an increase in the pressure inside said casing, said connecting ring incorporating a base forming a plate that can be projected onto said explosive load during the ignition of said fuse, said base being able to be fractured by the presence of pressure inside said body of said projectile.