Could the use of 'adapters' which fit into the chamber and swapping of the bolt, extractor and other parts allow firearms to use different calibers as long as the new cartridge is
Subcaliber Adapters | Load Data Article
Shoot any round through any firearm with subcaliber adapters - Carolina Sportsman
Miniature calibre (caliber) adapters and conversions
Caliber conversion sleeve - Wikipedia
X-Caliber Shotgun Gauge Adapter System - Athlon Outdoors
Cartridge Adapters | An Official Journal Of The NRA
these are shotgun adapters aka chamber reducers aka shotgun inserts and called by a few other names. they allow you to fire lower gauge (caliber) shotgun shells out of a larger bore gun. they are for use in break action type guns and won't (or shouldn't. i ...
Miniature calibre (caliber) adapters and conversions
Miniature calibre (caliber) adapters and conversions