US Patent 7997020 Gun barrel assembly

A firearm having a receiver housing an action-cycling mechanism, a barrel having a muzzle opening on a distal end, a shroud coaxially surrounding at least a portion of the barrel, the shroud having a distal portion extending beyond the muzzle opening defining a shroud front region having a distal end portion, a proximal portion extending proximally from the muzzle opening defining an annular region between the barrel and shroud, a front wall disposed at the distal end portion of the shroud, the front wall having an opening to allow passage of a projectile fired from the gun barrel, a firewall disposed in the annular region of the proximal portion of the shroud, the firewall moveable relative to the gun barrel between a forward, at-rest position, and a rearward, compressed position, the firewall mechanically engaged with the action cycling mechanism, and heat-dissipating fins in the annular region extending longitudinally along, and radially outward from, the gun barrel to the shroud, the fins defining channels, the firewall disposed in at least one of the channels. Gases generated during a fire compress the firewall rearward to operate the cycling mechanism.