Velocity and range of artillery vary directly with pressure of gunpowder or smokeless powder gasses pushing the shell out of a gun barrel; but a gun will be deformed or explode if chamber pressures strain a gun barrel beyond the elastic limit of the metal from which the barrel is made. Thickness of homogeneous cast metal gun barrels reached a useful limit at approximately one-half caliber. Additional thickness provided little practical benefit, since higher pressures generated cracks from the bore before the outer portion of the cylinder could respond, and those cracks would extend outward during subsequent firings.