what your acctualy "burning out" is the throat area. The best way to tell is your barrel is if it won't group anymore , this is coused by the throat being lengthened so far that the bullet has to make a huge jump to the lands.
Best thing to do is measure how far you can seat a bullet out to the lands,with a StonyPoint tool is the easiest way, then take another measure ment every couple hundred rounds and just keep a log of how far you throat is growing..
Just because your throat is shot out doesen't mean you barrel is ruined , you can have the barrel "set back" about a 1/4" and rechambered and that will usualy solve the problems as you are simply removing the burnt out section of barrel and replacing it with chamber.
I had a Savage heavy 308 barrel that was unbeleavably accurate for a factory barrel , once the throat had grown out to far I sent it off and had it set back about 3/16" and the chamber recut to 300WSM. now I have a great shooting 300WSM barrel that is as smooth as any custom barrel becasue it was lapped by some 4000 rounds and god only knows how many cleanings. all for just over a C-note
