Re: Question about rifle barrels.
I have shot rifles repeatedly and then scorched my fingertips on the barrel, no harm done. I have seen guys shoot SKS rifles till the handguard was smoking, again, no harm. It is not highly recommended to do so from an accuracy point of view, but it will not harm the rifle.
Unless you are shooting such overloaded ammo that you are beyond reasonable spec or huge case magnum calibers you will find it very hard to damage a gun barrel.