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
Cartridge Adapters | An Official Journal Of The NRA
X-CALIBER Survival-Rifle Gauge Adapter System - Soldier Systems Daily
Miniature calibre (caliber) adapters and conversions
Chiappa X-Cal 20 Ga Adapter Set of 4 Inserts Case
Shoot any round through any firearm with subcaliber adapters - Carolina Sportsman