Is there a concentric ridge and an elogation? Sounds like two different things.
First, get a chamber brush and really clean out your chamber, then find a friend with a bore scope or a local smith and have the chamber looked at. If for some reason you developed an area in the chamber (a concentric ridge and not overall case expansion) that is worn and is allowing the case to expand in that one area then the balance of the brass, it would be very hard to extract the case. Have you used any cleaning solutions using high concentrations of ammonia? Is this a carbon steel receiver or a stainless steel receiver?
Most Remingtons have been produced with Sammi spec chambers to insure that all commercial ammo will fit in the chamber and to keep the gun safe against excess pressures that could be caused by JAM, the projectile being jammed into the rifling. My Parker Hal 1200 has a tight chamber and not excessive free bore and with its twist it is great for .30 caliber projectiles up to 180 grainers, but 200s are tight do to the length of the projectile and anything over that once in the chamber with the bolt fully closed, would pull the case away from the projectile and leave it in the rifling if you tried to extract it. I found that out once the hard way.
In any case, with the kind of throat (free bore) that factory rifles like the 700 have, case expansion in length is pretty normal and it is hard to understand why that would make the fired round hard to extract. A smith should have a go/no go gauge to so you can check head space.
Bob