Do they have to do it - of course not. BUT, I still recall many years ago I bought a Remington shotgun. Every six months or so I would take it out of the safe and wipe if down. Each time I would get what looked like rust off of the barrel. No other guns and only on the barrel. The darn thing could have an oil film on it the size of Texan and I would still get the rust like film. After several years the bluing started looking thin in spots and generally nasty. The warranty was long expired. I sent a letter to Remington and they said that back then they had a problem with the bluing on some barrels and they would fix it under warranty, the warranty that had expired years ago! They did fix it and I am still talking about it. Something to think about is that the gun left the factory with the problem. Did they / do they have to fix it, of course not. But I would fix it if it was my company. Would I be mad if they did not fix my gun, no not really. Would I be happy if they did, OH YES. This happened over 10 years ago and I am still talking about it. That is inexpensive advertising.