The weakness of the breech @-@ loader was the obvious problem of sealing the breech . All guns are powered by the explosive conversion of gunpowder into gas . This explosion propels the shot or shell out of the front of the gun , but also imposes great stresses on the gun @-@ barrel . If the breech — which experiences some of the greatest forces in the gun — is not entirely secure , then there is a risk that either gas will discharge through the breech or that the breech will break . This in turn reduces the muzzle velocity of the weapon and can also endanger the gun crew . The Warrior 's Armstrong guns suffered from both problems ; the shells were unable to penetrate the 4 @.@ 5 in ( 118 mm ) armor of Gloire , while sometimes the screw which closed the breech flew backwards out of the gun on firing . Similar problems were experienced with the breech @-@ loading guns which became standard in the French and German navies .