AFAIK, the only commercial gun you cannot have a barrel changed on by your local gunsmith is the Browing A-bolt. The factory uses some kind of industrial super Loctite on the barrel threads that impedes its removal, and they say you need to return it to factory service for a new barrel. No idea why they did that?
Barrel life depends on conditions. About ten years ago, Sierra ballistics technician Kevin Thomas did an experiment shooting out stainless .308 barrels on Remington actions by using them in the company's normal QC testing process. Sierra keeps aside a special lot of 168 grain MatchKings that turned out to be more accurate than their normal production, and that they use as reference bullets in testing. He fired those in the six barrels he shot out while looking to see if cryo-treating or moly-coating did anything to extend barrel life? In the process he found the untreated barrels with untreated bullets went about 3500 rounds before he could detect beginning signs of the barrel being shot out. IIRC, Cryo-treating added 14%, (4000 rounds total), which is close to the roughly 20% it is credited with for extending the wear life of stainless tooling. Cryo-treating chrome-moly tool steel is usually claimed to double its wear resistance, and I am sorry Thomas didn't test some chrome-moly barrels to see if the matter applied there, as well. About 3000 rounds barrel life is what you hear service rifle match shooters talk about for .308.
I don't know if you've ever shot a barrel out, but the initial signs can disguise themselves pretty well. It comes in the form of a flyer you can't account for. Those just become more and more frequent until, about the time you are getting one every tenth shot, it finally dawns on you that the problem isn't you. When I shot out my first M1A barrel it happened like that. The fliers were a little over an moa off POA, so called X's instead scored 9's in slow fire. I would say it progressed from being one every 50 shots to one every 10 shot over a span of a couple or three hundred rounds. So you can see how shooters would blame themselves for errors that size until the frequency became great.
We have a competitive shooter on another forum who is a former Aberdeen Proving Grounds employee who conducted gun testing, among other things. He has a theory that hardened carbon residue is a wear factor and makes a good argument for it. He found barrels that shot out in a few thousand rounds in semi-auto fire could, contrary to intuition, go 15,000 or more when fired full auto, which keeps the non-metallic fouling warm and soft. The hammer forged 5R grade steel barrels Remington buys for the M24 sniper system have been reported to go 20,000 rounds, but the snipers clean more often than match competitors. Also, as mentioned above, the steel matters, and I don't know how the metallurgy of that steel compares to other barrel steels. It could be a significant contributor.