I hate to say this, but many Remington semi-auto and pump shooters don't clean their rifles well (or ever). In semi-autos, it's a bigger problem because chambers get baked by relatively hot gasses every time the case is ejected.
Because the rifle can't be cleaned from the breech with a conventional rod, those who clean from the muzzle don't realize that the chamber isn't adequately cleaned or protected by whatever oil is used to clean and protect the bore.
Many years ago, when working as a part-time gunsmith, I had several Remington 740s and 742s with rusty chambers. Sometimes the case remained stuck and the extractor tore a portion of the rim off, sometimes the whole case head. Those rifles usually come with a chamber brush that has a patch loop on the other end. Many are never used.
The owner of a "new" 742 confessed that he shot a box of ammo to sight-in, then hunted in the rain and never cleaned the gun, but put it away for the winter, spring, summer. The first shot in the fall resulted in the stuck case.
I tell this, because if bores aren't cleaned/protected, excessive friction increases pressures that can create excessive headspace. The stuck cases tell the tale of poor chamber maintenance and probably rusty bores. The rifles are probably fine as they come from the factory, but they're not foolproof...because fools are either so ingenious or just plain lazy.