deformation the stress no longer increases the equivalent stress flat lines in the plastic zone during autofrettage once the autofrettage pressure is relieved the outer hoop layers are left in a state of tension as they attempt to drive the permanently enlarged bore hoop layers back to their original size fig3 c shows the results that being in the compression of the surface of the bore upon firing a nearly constant equivalent stress is achieved through out the radius of the gun barrel the propulsion pressure overcomes the compression preload gun as shown in fig3 d autofrettage is distinct from the current pre stressed rail gun construction as typified by the designs shown in fig2 a and 2 b prior art first the bore 17 of the gas gun typically constructed of steel is fully capable of tolerating substantial tension this is in sharp contrast to the insulators 15 of the rail guns that must be bound in compression to prevent separation of the rails 12 from the insulator 15 second autofrettage achieves a favorable stress distribution throughout the structure the outer tensile containment structure of these rail guns exhibits the highest strain at the inner layers of the tensile containment structure using principles presented by autofrettage in gun construction as discussed above it has been discovered that modified designs of rail guns can incorporate principles of this phenomenon the present invention embodying a rail gun barrel defined by an elongated bore 31 shown at fig4 for passage of a projectile is explained as follows fig4 and 5 depict a preferred rail gun barrel 22 construction which comprises a pair of elongated generally parallel electrically conductive rails 23 and a pair of elongated generally parallel insulators 24 fig4 shows the gun wherein belleville containment disk 25 are in a non.