Custodian, with exceptions and most of those have been mentioned. I relined a Jeffrey Rook rifle because it had already been re-chambered to 25-20 WCF and the bore looked like a sewer pipe. I have forever regretted opening up the chambers on a Meffert drilling that otherwise was quite nice.

Kinda like cars, I hate resto mods and those god-awful low profile tires and 19 inch wheels on a 50's or 60's era car or pick-up are the worst.

Nitrox, "escutcheon" is the word you're looking for.