Built-up gun

An inner tube of metal stretches within its elastic limit under the pressure of confined powder gases to transmit stress to outer cylinders that are under tension.

[1] Concentric metal cylinders or wire windings are assembled to minimize the weight required to resist the pressure of powder gases pushing a projectile out of the barrel.

Velocity and range of artillery vary directly with pressure of gunpowder or smokeless powder gases pushing the shell out of a gun barrel.

A gun will deform (or explode) if chamber pressures strain the barrel beyond the elastic limit of the metal from which it is made.

[1] Thickness of homogeneous cast iron gun barrels reached a useful limit at approximately one-half caliber.

The forward part of the barrel may be tapered toward the muzzle because less strength is required for reduced pressures as the projectile approaches it.

Very large guns sometimes use shorter outer cylinders called hoops when manufacturing limitations make full length jackets impractical.

This melted metal is oxidized or blown out of the muzzle until the barrel is eroded to the extent shell dispersion becomes unacceptable.

Conical liners are tapered toward the muzzle for ease of removal from the breech end while limiting forward creep during firing.

In a procedure called autofrettage, a bored monoblock tube is filled with hydraulic fluid at pressures higher than the finished gun will experience during firing.