CLR in a chrome steel barrel will have to be thoroughly removed, as will many other bore cleaners after cleaning to avoid rusting. I suspect that if you put a good borescope camera down the tube that you'd find a lot of rust pitting. An old rifle that's been shot "quite a bit" as you say, would otherwise be pretty smooth in the bore, my 1898 Krag is almost like new. And while not accounting for some fire cracking, would not copper up near as much as a newly manufactured Savage for instance, which is known for having railroad track like rifling that loves to accumulate copper.

Rust pitting is not necessarily the end of barrel accuracy, as long as you aren't shooting in matches, but if it were mine I'd be looking for answers. Rust pitting inside the barrel can be removed completely with electrolysis, which won't hurt the blueing. All you need is a battery charger, a steel rod that will fit loosely inside the barrel so that it doesn't touch the barrel ( use tape, o-rings, etc to keep it from touching) and some Arm and Hammer wash soda from Wally World.