I have a cheap stainless steel take-off barrel from a 6.5CM AR-10 that I replaced because it was way over gassed.You didn't cause it with a jag. Not possible.
I have been toying with the idea of sacrificing that barrel to science and seeing if it would be possible to beat the crap out of the inside of the barrel using a jag with no bore guide or cleaning patch.
My guess is that there is no angle or amount of force that could be applied through a cleaning jag with well rounded edges to damage barrel steel. I would assume that land gouging would have to be caused by tool steel or something of a similar hardness.